improve CONTRIBUTING.rst to explain how/when to propose stories/specs

Expanding on the contributor guide, as discussed in the 11/21 IRC meeting.

http://eavesdrop.openstack.org/meetings/self_healing/2018/self_healing.2018-11-21-09.02.txt

Story: 2004536
Task: 28280

Change-Id: I5681d957232125c2f21a4d0fb6e9d467123f18e1

CONTRIBUTING.rst

@@ -6,13 +6,89 @@ Contributing to OpenStack's self-healing SIG
 
 If you would like to participate in discussions or contribute in any
 way to the design and development of self-healing in OpenStack, please
-first see:
+first see the following wiki to understand the SIG's mission, scope,
+and other supporting information:
 
   https://wiki.openstack.org/wiki/Self_healing_SIG
 
-Contributions to the use-cases and specifications in this repository
-are very welcome.  To contribute to this repository, you must follow
-the steps in this page:
+Many forms of contribution are valuable to the community, including but not
+limited to the following:
+
+- `Documentation of use cases <#use-cases>`_, including implementation details if available
+- `Design specs`_
+- `Code`_
+- `Discussions`_ on all the above and other topics
+
+Everyone is warmly encouraged to get involved in whatever capacity you
+see fit.
+
+Discussions
+-----------
+
+Discussions take place:
+
+- on `the openstack-discuss mailing list
+  <http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-discuss>`_
+  with ``[self-healing-sig]`` in the Subject header,
+- the `#openstack-self-healing IRC channel on Freenode
+  <http://eavesdrop.openstack.org/irclogs/%23openstack-self-healing/>`_
+  (including `meetings every fortnight
+  <http://eavesdrop.openstack.org/#Self-healing_SIG_Meeting>`_),
+- `the SIG's storyboard
+  <https://storyboard.openstack.org/#!/project/openstack/self-healing-sig>`_,
+- and in patch reviews.
+
+Links to all resources can also be found in the `SIG wiki section on
+community`_.
+
+.. _`SIG wiki section on community`: https://wiki.openstack.org/wiki/Self-healing_SIG#Community_Infrastructure_.2F_Resources
+
+Use cases
+---------
+
+The SIG serves to facilitate the discussion and documentation of self-healing
+use cases at all stages of development from a seed idea to a fully tested use
+case.
+
+To call attention to a use case, please start the discussion in `one
+of the established communication channels <#discussions>`_.
+
+Alternatively, directly submit a patch to document the use case,
+following the format laid out in the `template file
+<http://git.openstack.org/cgit/openstack/self-healing-sig/tree/use-cases/template.rst>`__
+in `the use-cases/ directory
+<http://git.openstack.org/cgit/openstack/self-healing-sig/tree/use-cases>`_
+of `the self-healing-sig repository
+<http://git.openstack.org/cgit/openstack/self-healing-sig>`_.
+
+See `Submitting a change`_ for more information.
+
+Design specs
+------------
+
+Design specs are proposed implementations of self-healing
+functionality across projects. To author a new design spec, please
+follow the format laid out in the `template file
+<http://git.openstack.org/cgit/openstack/self-healing-sig/tree/specs/template.rst>`__
+in `the specs/ directory
+<http://git.openstack.org/cgit/openstack/self-healing-sig/tree/specs>`_
+of `the self-healing-sig repository`_.
+
+See `Submitting a change`_ for more information.
+
+Code
+----
+
+`The self-healing-sig repository`_ also holds any relevant
+cross-project code, tests, and documentation that do not naturally
+belong in a single project repository.
+
+See `Submitting a change`_ for more information.
+
+Submitting a change
+-------------------
+
+To submit a change to this repository, please follow the steps in this page:
 
    http://docs.openstack.org/infra/manual/developers.html