Add HACKING.rst

Add information about hacking and testing the repository.

Change-Id: I48bc4e6342295a35959cbd796ac0be1fb08a9dd2

HACKING.rst

@@ -1,4 +1,26 @@
-openstack-doc-tools Style Commandments
+openstack-doc-tools style commandments
 ======================================
 
-Read the OpenStack Style Commandments http://docs.openstack.org/developer/hacking/
+- Step 1: Read the OpenStack Style Commandments
+  http://docs.openstack.org/developer/hacking/
+
+- Step 2: Read on
+
+Running tests
+-------------
+
+So far there are no tests included with the package but a test suite
+would be welcome!
+
+Since the openstack-doc-test tool is used for gating of the OpenStack
+documentation repositories, test building of these repositories with
+any changes done here.
+
+Testing can be done with simply a local install of
+openstack-doc-tools, then checking out the gated repositories and
+running: ``tox`` inside of each.
+
+The repositories gated by openstack-doc-tools are:
+* api-guide
+* openstack-manuals
+* operations-guide