doc: Link to github discussions, issues and pull request pages

This should hopefully take people to the right place if they bother to
read the documentation.

doc/pull-requests.rst

@@ -1,8 +1,13 @@
-Submitting Pull Requests
-========================
+Pull Requests & Issues
+======================
 
-XDG Desktop Portal uses GitHub pull requests to review contributions. Please be
-kind and patient as code reviews can be long and be minutious.
+XDG Desktop Portal uses GitHub to
+`discuss new portals and features <https://github.com/flatpak/xdg-desktop-portal/discussions>`_,
+`track issues <https://github.com/flatpak/xdg-desktop-portal/issues>`_ and
+`take contributions <https://github.com/flatpak/xdg-desktop-portal/pulls>`_.
+
+Please be kind and patient as code reviews can be long and be minutious, issue
+triage takes effort and everyone has limited time and resources.
 
 Before developing features or fixing bugs, please make sure you have done the
 following:
@@ -11,4 +16,4 @@ following:
 - The code has been tested.
 - All commit messages are properly formatted and commits squashed where
   appropriate.
-- You have included updates to all appropriate documentation.
+- You have included updates to all appropriate documentation.