Clarified naming convention for Cargo

Added a sentence that tells the user that using main.rs and/or lib.rs is required for Cargo.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/doc/trpl/hello-cargo.md b/src/doc/trpl/hello-cargo.md
index cc8747d1fa7..ee9c84a53b3 100644
--- a/src/doc/trpl/hello-cargo.md
+++ b/src/doc/trpl/hello-cargo.md
@@ -33,7 +33,8 @@ $ mv main.rs src/main.rs
 ```
 
 Note that since we're creating an executable, we used `main.rs`. If we
-want to make a library instead, we should use `lib.rs`.
+want to make a library instead, we should use `lib.rs`. This convention is required
+for Cargo to successfully compile our projects. 
 Custom file locations for the entry point can be specified
 with a [`[[lib]]` or `[[bin]]`][crates-custom] key in the TOML file described below.