Book: Write lint group descriptions

This removes the empty separate files for the different groups and adds
a single file giving short explanations for each group and what to
expect from those groups.

12 files changed, 106 insertions, 10 deletions

diff --git a/book/src/SUMMARY.md b/book/src/SUMMARY.md
index db937f95d22..95bdde7281c 100644
--- a/book/src/SUMMARY.md
+++ b/book/src/SUMMARY.md
@@ -5,15 +5,7 @@
 - [Installation](installation.md)
 - [Usage](usage.md)
 - [Configuration](configuration.md)
-- [Clippy's Lints](lints/README.md)
-    - [Correctness]()
-    - [Suspicious]()
-    - [Style]()
-    - [Complexity]()
-    - [Perf]()
-    - [Pendantic]()
-    - [Nursery]()
-    - [Cargo]()
+- [Clippy's Lints](lints.md)
 - [Continuous Integration](continuous_integration/README.md)
     - [Travis CI](continuous_integration/travis.md)
     - [GitHub Actions](continuous_integration/github_actions.md)
diff --git a/book/src/lints.md b/book/src/lints.md
new file mode 100644
index 00000000000..35e30960b56
--- /dev/null
+++ b/book/src/lints.md
@@ -0,0 +1,105 @@
+# Clippy's Lints
+
+Clippy offers a bunch of additional lints, to help its users write more correct
+and idiomatic Rust code. A full list of all lints, that can be filtered by
+category, lint level or keywords, can be found in the [Clippy lint
+documentation].
+
+This chapter will give an overview of the different lint categories, which kind
+of lints they offer and recommended actions when you should see a lint out of
+that category. For examples, see the [Clippy lint documentation] and filter by
+category.
+
+The different lint groups were defined in the [Clippy 1.0 RFC].
+
+## Correctness
+
+The `clippy::correctness` group is the only lint group in Clippy which lints are
+deny-by-default and abort the compilation when triggered. This is for good
+reason: If you see a `correctness` lint, it means that your code is outright
+wrong or useless and you should try to fix it.
+
+Lints in this category are carefully picked and should be free of false
+positives. So just `#[allow]`ing those lints is not recommended.
+
+## Suspicious
+
+The `clippy::suspicious` group is similar to the correctness lints in that it
+contains lints that trigger on code that is really _sus_ and should be fixed. As
+opposed to correctness lints, it might be possible that the linted code is
+intentionally written like it is.
+
+It is still recommended to fix code that is linted by lints out of this group
+instead of `#[allow]`ing the lint. In case you intentionally have written code
+that offends the lint you should specifically and locally `#[allow]` the lint
+and add give a reason why the code is correct as written.
+
+## Complexity
+
+The `clippy::complexity` group offers lints that give you suggestions on how to
+simplify your code. It mostly focuses on code that can be written in a shorter
+and more readable way, while preserving the semantics.
+
+If you should see a complexity lint, it usually means that you can remove or
+replace some code and it is recommended to do so. However, if you need the more
+complex code for some expressiveness reason, it is recommended to allow
+complexity lints on a case-by-case basis.
+
+## Perf
+
+The `clippy::perf` group gives you suggestions on how you can increase the
+performance of your code. Those lints are mostly about code that the compiler
+can't trivially optimize, but has to be written in a slightly different way to
+make the optimizer's job easier.
+
+Perf lints are usually easy to apply and it is recommended to do so.
+
+## Style
+
+The `clippy::style` group is mostly about writing idiomatic code. Because style
+is subjective, this lint group is the most opinionated warn-by-default group in
+Clippy.
+
+If you see a style lint, applying the suggestion usually makes your code more
+readable and idiomatic. But because we know that this is opinionated, feel free
+to sprinkle `#[allow]`s for style lints in your code or `#![allow]` a style lint
+on your whole crate if you disagree with the suggested style completely.
+
+## Pedantic
+
+The `clippy::pedantic` group makes Clippy even more _pedantic_. You can enable
+the whole group with `#![warn(clippy::pedantic)]` in the `lib.rs`/`main.rs` of
+your crate. This lint group is for Clippy power users that want an in depth
+check of their code.
+
+> _Note:_ Instead of enabling the whole group (like Clippy itself does), you may
+> want to cherry-pick lints out of the pedantic group.
+
+If you enable this group, expect to also use `#[allow]` attributes generously
+throughout your code. Lints in this group are designed to be pedantic and false
+positives sometimes are intentional in order to prevent false negatives.
+
+## Restriction
+
+The `clippy::restriction` group contains lints that will _restrict_ you from
+using certain parts of the Rust language. It is **not** recommended to enable
+the whole group, but rather cherry-pick lints that are useful for your code base
+and your use case.
+
+> _Note:_ Clippy will produce a warning if it finds a
+> `#![warn(clippy::restriction)]` attribute in your code!
+
+Lints from this group will restrict you in some way. If you enable a restriction
+lint for your crate it is recommended to also fix code that this lint triggers
+on. However, those lints are really strict by design and you might want to
+`#[allow]` them in some special cases, with a comment justifying that.
+
+## Cargo
+
+The `clippy::cargo` group gives you suggestions on how to improve your
+`Cargo.toml` file. This might be especially interesting if you want to publish
+your crate and are not sure if you have all useful information in your
+`Cargo.toml`.
+
+[Clippy lint documentation]: https://rust-lang.github.io/rust-clippy/
+[Clippy 1.0 RFC]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#lint-audit-and-categories
diff --git a/book/src/lints/README.md b/book/src/lints/README.md
deleted file mode 100644
index a2777e8f4d5..00000000000
--- a/book/src/lints/README.md
+++ /dev/null
@@ -1 +0,0 @@
-# Clippy's Lints
diff --git a/book/src/lints/cargo.md b/book/src/lints/cargo.md
deleted file mode 100644
index e69de29bb2d..00000000000
--- a/book/src/lints/cargo.md
+++ /dev/null
diff --git a/book/src/lints/complexity.md b/book/src/lints/complexity.md
deleted file mode 100644
index e69de29bb2d..00000000000
--- a/book/src/lints/complexity.md
+++ /dev/null
diff --git a/book/src/lints/correctness.md b/book/src/lints/correctness.md
deleted file mode 100644
index e69de29bb2d..00000000000
--- a/book/src/lints/correctness.md
+++ /dev/null
diff --git a/book/src/lints/deprecated.md b/book/src/lints/deprecated.md
deleted file mode 100644
index e69de29bb2d..00000000000
--- a/book/src/lints/deprecated.md
+++ /dev/null
diff --git a/book/src/lints/nursery.md b/book/src/lints/nursery.md
deleted file mode 100644
index e69de29bb2d..00000000000
--- a/book/src/lints/nursery.md
+++ /dev/null
diff --git a/book/src/lints/pedantic.md b/book/src/lints/pedantic.md
deleted file mode 100644
index e69de29bb2d..00000000000
--- a/book/src/lints/pedantic.md
+++ /dev/null
diff --git a/book/src/lints/perf.md b/book/src/lints/perf.md
deleted file mode 100644
index e69de29bb2d..00000000000
--- a/book/src/lints/perf.md
+++ /dev/null
diff --git a/book/src/lints/restriction.md b/book/src/lints/restriction.md
deleted file mode 100644
index e69de29bb2d..00000000000
--- a/book/src/lints/restriction.md
+++ /dev/null
diff --git a/book/src/lints/style.md b/book/src/lints/style.md
deleted file mode 100644
index e69de29bb2d..00000000000
--- a/book/src/lints/style.md
+++ /dev/null