Edited contribution recognition section of contributing.md for readability and fixed a typo.

Author: jspeda

CONTRIBUTING.md

@@ -40,7 +40,7 @@ Issue the PR to the [master](https://github.com/webpack/webpack.js.org/tree/mast
 
 ## Contribution Recognition
 
-Any document that you edit, you can choose to add your GitHub username at the top of the document for recognition:
+You can choose to add your GitHub username for recognition at the top of any markdown document you edit:
 
 **example.md**
 
@@ -59,7 +59,8 @@ contributors:
 
 ```
 
-This will add your name and GitHub profile photo to the document in production. This is a great way to own the awesome work that you do and encourage that you remember to do this in your PR's.
+This will add your name and GitHub profile photo to the document in production. It's a great way to own the awesome work that you do and we encourage you to
+do this in your PRs.
 
 
 ## Thank you