doc: add link to ipython on github

docs/source/development/contributing.txt

@@ -8,8 +8,9 b' 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.
+(Github Ipython Repository: [IPyGithub]_) 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
@@ -80,3 +81,4 b" moment to read it (it's short but very informative)."
 
 .. [Git] The Git version control system. http://git-scm.com
 .. [Github.com] Github.com. http://github.com
+.. [IPyGithub] IPython repository on github. https://github.com/ipython/ipython