Add a CONTRIBUTING file

GitHub likes repos to have a CONTRIBUTING file. It will use this to
point people to the right place for how to contribute to this project.

Change-Id: Iad714c168dd8c476d8f99f131e3b7a998d165fc5
diff --git a/CONTRIBUTING.rst b/CONTRIBUTING.rst
new file mode 100644
index 0000000..a89ad94
--- /dev/null
+++ b/CONTRIBUTING.rst
@@ -0,0 +1,17 @@
+If you would like to contribute to the development of OpenStack, you must
+follow the steps in this page:
+
+   https://docs.openstack.org/infra/manual/developers.html
+
+If you already have a good understanding of how the system works and your
+OpenStack accounts are set up, you can skip to the development workflow
+section of this documentation to learn how changes to OpenStack should be
+submitted for review via the Gerrit tool:
+
+   https://docs.openstack.org/infra/manual/developers.html#development-workflow
+
+Pull requests submitted through GitHub will be ignored.
+
+Bugs should be filed on Launchpad, not GitHub:
+
+   https://bugs.launchpad.net/tempest