Update README.md

Add in contribution instruction

Author: jguomoto

README.md

@@ -22,3 +22,30 @@ First please take a look at our [FAQ](http://stackoverflow.com/questions/tagged/
 If you have general API questions related to Tango, we encourage you to post your question to our [stack overflow page](http://stackoverflow.com/questions/tagged/google-project-tango).
 
 You are also welcome to visit [Project Tango Developer website](https://developers.google.com/project-tango/) to learn more about general concepts and other information about the project.
+
+<h2>Contribution</h2>
+
+Want to contribute? Great! First, read this page (including the small print at the end).
+
+#### Before you contribute
+Before we can use your code, you must sign the
+[Google Individual Contributor License Agreement](https://developers.google.com/open-source/cla/individual?csw=1)
+(CLA), which you can do online. The CLA is necessary mainly because you own the
+copyright to your changes, even after your contribution becomes part of our
+codebase, so we need your permission to use and distribute your code. We also
+need to be sure of various other things—for instance that you'll tell us if you
+know that your code infringes on other people's patents. You don't have to sign
+the CLA until after you've submitted your code for review and a member has
+approved it, but you must do it before we can put your code into our codebase.
+Before you start working on a larger contribution, you should get in touch with
+us first through the issue tracker with your idea so that we can help out and
+possibly guide you. Coordinating up front makes it much easier to avoid
+frustration later on.
+
+#### Code reviews
+All submissions, including submissions by project members, require review. We
+use Github pull requests for this purpose.
+
+#### The small print
+Contributions made by corporations are covered by a different agreement than
+the one above, the Software Grant and Corporate Contributor License Agreement.