Fix links to contributing guidelines

CONTRIBUTING.md

@@ -15,7 +15,7 @@ for support - use our [Wagtail support group](https://groups.google.com/forum/#!
 ## New code
 
 Please review the 
-[coding guidelines](http://docs.wagtail.io/en/latest/contributing/developing.html#coding-guidelines). 
+[contributing guidelines](http://docs.wagtail.io/en/latest/contributing/index.html). 
 You might like to start by checking issues with the 
 [difficulty:Easy](https://github.com/torchbox/wagtail/labels/difficulty%3AEasy) label.
 

README.rst

@@ -76,6 +76,6 @@ Contributing
 ~~~~~~~~~~~~
 If you're a Python or Django developer, fork the repo and get stuck in! We run a separate group for developers of Wagtail itself at https://groups.google.com/forum/#!forum/wagtail-developers (please note that this is not for support requests).
 
-You might like to start by reviewing the `coding guidelines <http://docs.wagtail.io/en/latest/contributing/developing.html#coding-guidelines>`_ and checking issues with the `difficulty:Easy <https://github.com/torchbox/wagtail/labels/difficulty%3AEasy>`_ label.
+You might like to start by reviewing the `contributing guidelines <http://docs.wagtail.io/en/latest/contributing/index.html>`_ and checking issues with the `difficulty:Easy <https://github.com/torchbox/wagtail/labels/difficulty%3AEasy>`_ label.
 
 We also welcome translations for Wagtail's interface. Translation work should be submitted through `Transifex <https://www.transifex.com/projects/p/wagtail/>`_.