point to code, issues and support in devel section

real story: users that are also developpers expect to find out where
to submit issues and pull requests in the development section, but
couldn't. add some meat there and point to the support section for
everything else.

docs/development.rst

@@ -10,6 +10,15 @@ This chapter will get you started with |project_name| development.
 |project_name| is written in Python (with a little bit of Cython and C for
 the performance critical parts).
 
+Code and issues
+---------------
+
+Code is stored on Github, in the `Borgbackup organization
+<https://github.com/borgbackup/borg/>`_. `Issues
+<https://github.com/borgbackup/borg/issues>`_ and `pull requests
+<https://github.com/borgbackup/borg/pulls>`_ should be sent there as
+well. See also the :ref:`support` section for more details.
+
 Style guide
 -----------