Update contribution_guide.rst (pytorch#64142)

Summary:
Grammatical update.

Fixes #{issue number}

Pull Request resolved: pytorch#64142

Reviewed By: mruberry

Differential Revision: D30639394

Pulled By: ezyang

fbshipit-source-id: cf1a4dfbd8e34b0772f1b09f5d820278e8ef8574

docs/source/community/contribution_guide.rst

@@ -200,8 +200,8 @@ Triaging issues
 ~~~~~~~~~~~~~~~
 
 If you feel that an issue could benefit from a particular tag or level
-of complexity comment on the issue and share your opinion. If you
-feel an issue isn't categorized properly comment and let the team know.
+of complexity, comment on the issue and share your opinion. If you
+feel an issue isn't categorized properly, comment and let the team know.
 
 About open source development
 -----------------------------