added documentation github repo details (#592)

diff --git a/source/index.rst b/source/index.rst
index 8bc3708..b9b369e 100644
--- a/source/index.rst
+++ b/source/index.rst
@@ -51,6 +51,7 @@
    Apache CloudStack web site <http://cloudstack.apache.org/>
    Apache CloudStack Source Code <http://cloudstack.apache.org/downloads.html>
    Apache CloudStack on GitHub <https://github.com/apache/cloudstack>
+   Apache CloudStack Documentation on GitHub <https://github.com/apache/cloudstack-documentation>