[ussuri][goal] Update contributor documentation

This patch updates/adds the contributor documentation to follow
the guidelines of the Ussuri cycle community goal[1].

[1] https://governance.openstack.org/tc/goals/selected/ussuri/project-ptl-and-contrib-docs.html
Story: #2007236
Task: #38554

Change-Id: Ib54b16543eb428087555cd3411bae51244d1aa65
diff --git a/doc/source/index.rst b/doc/source/index.rst
index ab994d1..630cccc 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -56,6 +56,16 @@
 
    supported_version
 
+For Contributors
+================
+
+* If you are a new contributor to Tempest please refer: :doc:`contributor/contributing`
+
+.. toctree::
+   :hidden:
+
+   contributor/contributing
+
 Developers Guide
 ================
 
@@ -104,4 +114,4 @@
   * :ref:`Tempest document search <search>`: Search the contents of this document.
 
 * `OpenStack wide search <https://docs.openstack.org>`_: Search the wider
-  set of OpenStack documentation, including forums.
\ No newline at end of file
+  set of OpenStack documentation, including forums.