Linking README to wiki.

README.md

-This is a read-only copy of the canonical Blockly repository [https://code.google.com/p/blockly/].
-Please do not issue pull requests here.
+# Blockly
+
+Google's Blockly is a web-based, graphical programming editor.  Users can drag
+blocks together to build a programs.  All code is free and open source.
+
+*The project page is [https://github.com/google/blockly/wiki]*