Updated dev docs with information about commit messages.

docs/source/development/contributing.txt

@@ -1,52 +1,82
 .. _contributing:
 
 ============================
 How to contribute to IPython
 ============================
 
 Overview
 ========
 
 IPython development is done using Git [Git]_ and Github.com [Github.com]_.
 This makes it easy for people to contribute to the development of IPython.
 There are several ways in which you can join in.
 
 
 Merging a branch into trunk
 ===========================
 
 Core developers, who ultimately merge any approved branch (from themselves,
 another developer, or any third-party contribution) will typically use
 :command:`git merge` to merge the branch into the trunk and push it to the main
 Git repository. There are a number of things to keep in mind when doing this,
 so that the project history is easy to understand in the long run, and that
 generating release notes is as painless and accurate as possible.
 
 * When you merge any non-trivial functionality (from one small bug fix to a
   big feature branch), please remember to always edit the appropriate file in
   the :ref:`What's new <whatsnew_index>` section of our documentation.
   Ideally, the author of the branch should provide this content when they
   submit the branch for review. But if they don't it is the responsibility of
   the developer doing the merge to add this information.
 
 * When merges are done, the practice of putting a summary commit message in
   the merge is *extremely* useful. It is probably easiest if you simply use
   the same list of changes that were added to the :ref:`What's new
   <whatsnew_index>` section of the documentation.
 
 * It's important that we remember to always credit who gave us something if
   it's not the committer. In general, we have been fairly good on this front,
   this is just a reminder to keep things up. As a note, if you are ever
   committing something that is completely (or almost so) a third-party
   contribution, do the commit as::
   
-    $ git commit --author="Someone Else"
+    $ git commit --author="Someone Else <[e-mail]>"
 
   This way it will show that name separately in the log, which makes it even
   easier to spot. Obviously we often rework third party contributions
-  extensively ,but this is still good to keep in mind for cases when we don't
+  extensively, but this is still good to keep in mind for cases when we don't
   touch the code too much.
 
 
 .. [Git] The Git version control system. 
 .. [Github.com] Github.com. http://github.com
+
+
+Commit messages
+===============
+
+Good commit messages are very important; they provide a verbal account of what
+happened that is often invaluable for anyone trying to undestand the intent of
+a commit later on (including the original author!).  And git's log command is a
+very versatile and powerful tool, capable of extracting a lot of information
+from the commit logs, so it's important that these logs actually have useful
+information in them.
+
+In short, a commit message should have the form::
+
+  One line summary.
+        <THIS LINE MUST BE LEFT BLANK>
+  More detailed description of what was done, using multiple lines and even
+  more than one paragraph if needed.  For very simple commits this may not be
+  necessary, but non-trivial ones should always have it.
+
+  Closes gh-NNN.  # if the commit closes issue NNN on github.
+
+This format is understood by many git tools that expect a *single line*
+summary, so please do respect it.
+
+An excellent reference on commits message is `this blog post`_, please take a
+moment to read it (it's short but very informative).
+
+.. _this blog post: http://who-t.blogspot.com/2009/12/on-commit-messages.html
+