Added documentation on how to use this repository

Author: siddhi

README.md

@@ -0,0 +1,24 @@
+Test Driven Python Development
+==============================
+
+This repository contains the code for the book `Test Driven Python Development <http://www.amazon.in/Test-Driven-Python-Development-Siddharta-Govindaraj/dp/1783987928/>`. 
+
+How to use this repository
+--------------------------
+
+The repository has tags, so you can get the code for the individual chapters by choosing the appropriate tag.
+
+**If you are familiar with using git & github**: Clone this repository, then look at tags to get the point in the code you want to go to. Checkout the appropriate tag on your local repository to get to that particular state of the code.
+
+**If you have not used github before**: Look at the `list of tags <https://github.com/siddhi/test_driven_python/tags>`, and click the *zip link* for the point in the code that you are interested in. This will download the code for that particular commit as a zip file. Unzip this file into your project folder and work from there.
+
+Notes
+-----
+
+* Python 2.6+ compatible version of the code is available on it's own branch here - https://github.com/siddhi/test_driven_python/tree/py2.6
+* Some readers have submitted contributions to this repository. You can access the code with these contributions in the *contrib* branch - https://github.com/siddhi/test_driven_python/tree/contrib
+
+Submitting contributions
+------------------------
+
+If you would like to submit changes to this repository, checkout the *contrib* branch, make changes and submit a pull request. I will be happy to merge the changes in.