Add manpage excerpt about new filetypes/enhancements

CONTRIBUTING.md

@@ -2,6 +2,17 @@
 
 Before you report an issue, please consult the [FAQ](http://beyondgrep.com/documentation/ack-2.12-man.html#faq).
 
+# Asking to add a new filetype, or any enhancement
+
+From the man page:
+
+   All enhancement requests MUST first be posted to the ack-users mailing list at <http://groups.google.com/group/ack-users>.  I will not consider a request without it first getting seen by other ack users.  This includes
+   requests for new filetypes.
+
+   There is a list of enhancements I want to make to ack in the ack issues list at Github: <https://github.com/petdance/ack2/issues>
+
+   Patches are always welcome, but patches with tests get the most attention.
+
 # Reporting an Issue
 
 If you have an issue with ack, please add the following to your ticket: