[Issue wevote#479] Update contributing documentation index.md

The index.md for our Contributing docs was empty. This commit adds a table of contents to help users navigate.

Closes issue wevote#479.

Author: nicogreenarry

docs/contributing/index.md

@@ -3,11 +3,18 @@
 <!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
 ## Contents
 
-- [](#)
-
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 
+Start here:
 
+1. [Our Culture and Philosophy](CONTRIBUTING_PHILOSOPHY.md)
+1. [Coding Standards](CONTRIBUTING_STANDARDS.md)
+1. `[Optional]` [What the Heck is a Pull Request?](PULL_REQUEST_BACKGROUND.md)
+1. [Before Your First Pull Request](PULL_REQUEST_SETUP.md)
+1. [Creating a Pull Request](CREATING_PULL_REQUEST.md)
+1. [Pull Request Tips & Tricks](PULL_REQUEST_ADVANCED.md)
+1. [Troubleshooting Pull Request Problems](PULL_REQUEST_TROUBLESHOOTING.md)
+1. [Approving Pull Requests](APPROVING_PULL_REQUESTS.md)