Add clarity to name of file being used in library example.

Author: wparad

src/crates/lib.md

@@ -2,6 +2,7 @@
 
 Let's create a library, and then see how to link it to another crate.
 
+In `rary.rs`:
 ```rust,ignore
 pub fn public_function() {
     println!("called rary's `public_function()`");
@@ -29,4 +30,4 @@ crate file, but this default name can be overridden by passing
 the `--crate-name` option to `rustc` or by using the [`crate_name`
 attribute][crate-name].
 
-[crate-name]: ../attribute/crate.md
+[crate-name]: ../attribute/crate.md