update readme

README.md

@@ -1,8 +1,12 @@
 simple-virtual-machine
 ======================
 
-A simple VM for a talk on building VMs.
+A simple VM for a talk on building VMs in Java. See [video](https://www.youtube.com/watch?v=OjaAToVkoTw) and [slides](http://www.slideshare.net/parrt/how-to-build-a-virtual-machine).
 
-[A C implementation](https://github.com/codyebberson/vm)
+There are two branches:
+
+* [master](https://github.com/parrt/simple-virtual-machine). Basic instructions only (no function calls).
+* [add-functions](https://github.com/parrt/simple-virtual-machine/tree/add-functions). Includes CALL/RET instructions, runs factorial test function.
+* [split-stack](https://github.com/parrt/simple-virtual-machine/tree/split-stack). Split into operand stack and function call stack.
 
-This branch supports function call/return.
+[A C implementation](https://github.com/codyebberson/vm)