Add README

README

+Welcome to the Source code of MIT App Inventor.
+
+You can learn more about MIT App Inventor at http://appinventor.mit.edu.
+
+This code is designed to be run in Google's App Engine. MIT runs a
+public instance that all are welcome to use to build App Inventor
+Applications. You do not need to compile or use this code if you wish
+to build MIT App Inventor applications.
+
+We provide this code for reference and for experienced people who wish
+to operate their own App Inventor instance.
+
+To build: cd to appinventor and type "ant."
+
+This code is tested and known to work with Sun Java 6. There are
+issues with using OpenJDK.