Update the testing doc to be more clear and include dynamic link

Fixed some typos and changed the link to the link to crates-and-modules to be dynamic.

Author: kickinbahk

src/doc/trpl/testing.md

@@ -505,4 +505,5 @@ you add more examples.
 We haven’t covered all of the details with writing documentation tests. For more,
 please see the [Documentation chapter](documentation.html)
 
-One final note: Tests *cannot* be run on the binary (main) file. To see more on file arrangement see the [Crates and Modules](https://doc.rust-lang.org/stable/book/crates-and-modules.html) Section
+One final note: Tests *cannot* be run on a binary file. To see more on file arrangement see the [Crates and Modules](crates-and-modules.html) section.
+