Include link to "Crates and Modules" guide

SETUP.md

@@ -2,7 +2,7 @@
 
 Refer to the exercism help page at http://help.exercism.io/getting-started-with-rust.html for Rust installation and learning resources.
 
-## Running the Tests
+## Writing the Code
 
 Execute the tests with:
 
@@ -11,3 +11,5 @@ $ cargo test
 ```
 
 All but the first test have been ignored.  After you get the first test to pass, remove the ignore flag (`#[ignore]`) from the next test and get the tests to pass again.  The test file is located in the `tests` directory.   You can also remove the ignore flag from all the tests to get them to run all at once if you wish.
+
+Make sure to read the [Crates and Modules](http://doc.rust-lang.org/stable/book/crates-and-modules.html) chapter if you haven't already, it will help you with organizing your files.