docs: Add a minimal Tempest guide

This can be fleshed out more in the future, including with information
about managing plugins, but this is a start.

Change-Id: I1094d093b704e37370e3e434ebf3697954e99da3
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

Author: stephenfin

doc/source/tempest.rst

@@ -0,0 +1,25 @@
+=======
+Tempest
+=======
+
+`Tempest`_ is the OpenStack Integration test suite. It is installed by default
+and is used to provide integration testing for many of the OpenStack services.
+Just like DevStack itself, it is possible to extend Tempest with plugins. In
+fact, many Tempest plugin packages also include DevStack plugin to do things
+like pre-create required static resources.
+
+The `Tempest documentation <Tempest>`_ provides a thorough guide to using
+Tempest. However, if you simply wish to run the standard set of Tempest tests
+against an existing deployment, you can do the following:
+
+.. code-block:: shell
+
+    cd /opt/stack/tempest
+    /opt/stack/data/venv/bin/tempest run ...
+
+The above assumes you have installed DevStack in the default location
+(configured via the ``DEST`` configuration variable) and have enabled
+virtualenv-based installation in the standard location (configured via the
+``USE_VENV`` and ``VENV_DEST`` configuration variables, respectively).
+
+.. _Tempest: https://docs.openstack.org/tempest/latest/