DOC: Edit contributing to docs section

Author: willingc

doc/source/contributing.rst

@@ -262,8 +262,9 @@ after updating.
 Contributing to the documentation
 =================================
 
-If you're not the developer type, contributing to the documentation is still of
-huge value. You don't even have to be an expert on *pandas* to do so! In fact,
+Contributing to the documentation benefits everyone who uses *pandas*.
+We encourage you to help us improve the documentation, and
+you don't have to be an expert on *pandas* to do so! In fact,
 there are sections of the docs that are worse off after being written by
 experts. If something in the docs doesn't make sense to you, updating the
 relevant section after you figure it out is a great way to ensure it will help