copyedits to pull requests section

docs/contributing.rst

@@ -25,14 +25,14 @@ Please put feature requests on our `issue tracker`_.
 Pull requests
 -------------
 
-When you submit a PR you'll see a template that pops up - it's reproduced
+When you submit a PR, you'll see a template that pops up - it's reproduced
 here.
 
 
 - Provide a general summary of your changes in the Title
 - Describe your changes in detail
-- If the PR closes an issue make sure include e.g., `fix #4` or similar,
-  or if just relates to an issue make sure to mention it like `#4`
+- If the PR closes an issue, make sure to include, e.g., `fix #4` or similar,
+  or if it just relates to an issue, make sure to mention it like `#4`
 - If introducing a new feature or changing behavior of existing
   methods/functions, include an example if possible to do in brief form
 - Did you remember to include tests? Unless you're changing docs/grammar,