expand "how to contribute"

content/community.txt

@@ -146,10 +146,35 @@ It is best to base your work on the latest version of Kwant::
 
     git clone http://git.kwant-project.org/kwant
 
-Then you can modify the code, and build Kwant and the documentation as
+Then you can build Kwant and the documentation as
 described in the `build instructions
 </doc/1.0/pre/install.html#building-and-installing-from-source>`_.
 
+The Kwant git repository has two main branches: The branch *master*
+contains the development towards the next release.  The branch *stable* contains
+the most recent release that is considered stable, and only bugfixes are applied
+to it.
+
+We recommend that you keep your changes on a separate `topic branch
+<https://www.kernel.org/pub/software/scm/git/docs/gitworkflows.html#_topic_branches>`_
+that starts at *master*.  To create such a branch, use the command::
+
+    git checkout -b my_topic_branch master
+
+Once you have something that you would like to share, let us know about it by
+posting to kwant-devel@kwant-project.org.  We are happy to receive useful
+contributions in any reasonable way: you can send patches to the mailing list,
+make your git repository available on the web (you could use a service like
+github), or even directly send the file that you modified.
+
+The recommended way is sending patches to the mailing list.  (This avoids
+confusion by publishing unfinished git branches and allows code review.)  See
+this `example of usage
+<https://kernel.org/pub/software/scm/git/docs/git-send-email.html#_example>`_
+and this `git send-email howto
+<http://www.freedesktop.org/wiki/Software/PulseAudio/HowToUseGitSendEmail/>`_,
+it’s easy.
+
 Some things to keep in mind:
 
 * Please keep the code consistent by adhering to the prevailing naming and
@@ -163,6 +188,8 @@ Some things to keep in mind:
 * Write tests for all the important functionality you add.  Be sure not to
   break existing tests.
 
+* Create a logical sequence of commits with clear commit messages.
+
 A useful trick for working on the source code is to build in-place so that there
 is no need to re-install after each change.  This can be done with the following
 command ::