Update instructions to match modern install/build process

README.md

@@ -4,20 +4,20 @@ Learn about the Elm programming language at [elm-lang.org](http://elm-lang.org/)
 
 ## Install
 
-Follow [these instructions][installer] if you just want to use Elm. To build
-the compiler from source, run the following commands:
+Follow [these instructions][installer] to use Elm on your machine. Be sure to use
+the platform specific installers if you are on Mac or Windows. It's way easier!
 
  [installer]: https://github.com/elm-lang/elm-platform/blob/master/README.md#elm-platform 
 
-```bash
-git clone https://github.com/elm-lang/Elm.git
-cd Elm
-cabal configure
-cabal build
-```
+## Build from source / Contribute
 
-This will build the compiler in `/dist/build/elm/elm` but it will not be on
-your PATH.
+Use [this script][build] to build the entire Elm Platform from source: the compiler,
+REPL, package manager, and reactor. Be sure to read all the instructions to learn
+how the script works and what your workflow will be like.
+
+[build]: https://github.com/elm-lang/elm-platform/blob/master/src/BuildFromSource.hs
+
+## Help
 
 If you are stuck, email
 [the list](https://groups.google.com/forum/?fromgroups#!forum/elm-discuss)