Add a Contribute.md file (issue #94)

See https://github.com/blog/1184-contributing-guidelines

Contributing.md

@@ -0,0 +1,18 @@
+Issues
+======
+
+A good issue includes a [short, self contained, correct example](http://sscce.org/) of the problem, something like:
+
+    assert github.Github().get_user("jacquev6").name == "Vincent Jacques"
+
+It is even better if you provide the debug logs associated with your issue.
+Enable them with `github.enable_console_debug_logging()` and copy them in the body of the issue.
+Warning, you may want to remove some private information (authentication information is removed, but there may be private stuff in the messages)
+
+If for any reason you are not able to provide, open your issue anyway and we will see what is needed to solve your problem.
+
+Pull requests
+=============
+
+PyGithub follows [pep8 Style Guide for Python Code](http://www.python.org/dev/peps/pep-0008/) except for line length.
+So if you do heavy modifications, please check your code with [pep8 Python style guide checker](http://pypi.python.org/pypi/pep8), by running `pep8 --ignore=E501 github`.