update readme to add a link to contributing page

README.rst

@@ -468,7 +468,9 @@ The `projects <https://github.com/microsoft/dowhy/projects>`_ page lists the nex
 Contributing
 ============
 
-This project welcomes contributions and suggestions.  Most contributions require you to agree to a
+This project welcomes contributions and suggestions. For a guide to contributing and a list of all contributors, check out `CONTRIBUTING.md <https://github.com/microsoft/dowhy/blob/master/CONTRIBUTING.md>`_.
+
+Most contributions require you to agree to a
 Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us
 the rights to use your contribution. For details, visit https://cla.microsoft.com.