Remove reference to `hello_world.rs` in TRPL §2.2

When reading this paragraph, the beginning Rust programmer is starting
to write a Hello World program.  We have just told her to name the file
`main.rs`, and immediately afterward, a `hello_world.rs` is mentioned.
I changed this to an unrelated filename (incidentally one that appears
in this repository) to make it clear that this is just an example.
Also, wording it as a declarative sentence rather than an imperative one
further separates it from the Hello World instructions in this section.

0 files changed, 0 insertions, 0 deletions