docs: mention the contributing guide

Change-Id: I3f35c7bfa652fca9d32a2476b979415f8f5150c7
refs: #4415
diff --git a/docs/index.rst b/docs/index.rst
index 9bc19ef..4903931 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -46,6 +46,10 @@
   A comprehensive guide to the design and implementation of NFD. The developer's guide also contains
   suggestions and hints for anyone wanting to modify or extend NFD.
 
+* `NDN Software Contributor's Guide
+  <https://github.com/named-data/NFD/blob/master/CONTRIBUTING.md>`__
+  (guide for newcomers to the NDN community of software)
+
 * `NFD Wiki <https://redmine.named-data.net/projects/nfd/wiki>`_
 
   + `NFD Management protocol <https://redmine.named-data.net/projects/nfd/wiki/Management>`_