Various documentation updates focused around surfacing feedback article

Summary:
missed doing this for phame, so i poked around a bit and added it to
similar verbage as well as to a few "Next Steps" where I thought the feedback
might be provocative.

Test Plan: read the docs

Reviewers: vrana, epriestley

Reviewed By: epriestley

CC: aran

Differential Revision: https://secure.phabricator.com/D2220

src/docs/userguide/diffusion.diviner

@@ -144,4 +144,11 @@ You can add new classes which will extend or enhance Diffusion's ability to
 parse commit messages.
 
 TODO: This is an advanced feature which doesn't currently have documentation and
-isn't terribly stable.
+isn't terribly stable.
+
+= Next Steps =
+
+  - Learn about creating a symbol index at 
+    @{article:Diffusion User Guide: Symbol Indexes}; or
+  - give us feedback at @{article:Give Feedback! Get Support!}.
+