Note in readme that albacore 2.0 isn't supported

Since albacore moved to https://github.com/Albacore/albacore, a version 2.0 has been released in which the file structure is a little different. I don't know enough rake/ruby to be able to contribute to updating the build scripts, but I can at least help others figure out how to build the project.

This didn't take me all the way - the rake build still failed - but after installing this version of albacore I could at least get far enough to build in Visual Studio =)