Added details about CLA for contributions to the docs.

Author: jgeewax

docs/index.rst

@@ -50,3 +50,19 @@ The library is open source
 and `lives on GitHub <https://github.com/jgeewax/gcloud>`_.
 Open an issue
 or fork the library and submit a pull request.
+
+Keep in mind that before we can accept any pull requests
+we have to jump through a couple of legal hurdles,
+primarily a Contributor License Agreement (CLA):
+
+- **If you are an individual writing original source code**
+  and you're sure you own the intellectual property,
+  then you'll need to sign an `individual CLA
+  <http://code.google.com/legal/individual-cla-v1.0.html>`_.
+- **If you work for a company that wants to allow you to contribute your work**,
+  then you'll need to sign a `corporate CLA
+  <http://code.google.com/legal/corporate-cla-v1.0.html>`_.
+
+Follow either of the two links above to access the appropriate CLA
+and instructions for how to sign and return it.
+Once we receive it, we'll be able to accept your pull requests.