Add basic user guide (#79)

diff --git a/docs/index.rst b/docs/index.rst
index e7a17e3..c0cbdbf 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -1,22 +1,62 @@
-Welcome to ``google-auth``'s documentation!
-===========================================
-
-Contents:
+google-auth
+===========
 
 .. toctree::
+   :hidden:
    :maxdepth: 2
 
-   reference/modules
+   user-guide
+   Reference <reference/modules>
 
-Reference documentation
-=======================
+google-auth is the Google authentication library for Python. This library
+provides the ability to authenticate to Google APIs using various methods. It
+also provides integration with several HTTP libraries.
 
-The :doc:`reference documentation <reference/modules>` details the complete API for :mod:`google.auth` and :mod:`google.oauth2`.
+- Support for Google :func:`Application Default Credentials <google.auth.default>`.
+- Support for signing and verifying :mod:`JWTs <google.auth.jwt>`.
+- Support for Google :mod:`Service Account credentials <google.oauth2.service_account>`.
+- Support for :mod:`Google Compute Engine credentials <google.auth.compute_engine>`.
+- Support for :mod:`Google App Engine standard credentials <google.auth.app_engine>`.
+- Support for various transports, including
+  :mod:`Requests <google.auth.transport.requests>`,
+  :mod:`urllib3 <google.auth.transport.urllib3>`, and
+  :mod:`gRPC <google.auth.transport.grpc>`.
 
-Indices and tables
-==================
+Installing
+----------
 
-* :ref:`genindex`
-* :ref:`modindex`
-* :ref:`search`
+google-auth can be installed with `pip`_::
 
+    $ pip install --upgrade google-auth
+
+google-auth is open-source, so you can alternatively grab the source code from
+`GitHub`_ and install from source.
+
+.. _pip: https://pip.pypa.io
+.. _GitHub: https://github.com/GoogleCloudPlatform/google-auth-library-python
+
+Usage
+-----
+
+The :doc:`user-guide` is the place to go to learn how to use the library and
+accomplish common tasks.
+
+The :doc:`Module Reference <reference/modules>` documentation provides API-level documentation.
+
+License
+-------
+
+google-auth is made available under the Apache License, Version 2.0. For more
+details, see `LICENSE`_
+
+.. _LICENSE:
+    https://github.com/GoogleCloudPlatform/google-auth-library-python/LICENSE
+
+Contributing
+------------
+
+We happily welcome contributions, please see our `contributing`_ documentation
+for details.
+
+.. _contributing:
+    https://github.com/GoogleCloudPlatform/google-auth-library-python/CONTRIBUTING.rst