Add the Windows wiki link to the README

Author: José Valim

README.md

@@ -12,6 +12,8 @@ If you want to contribute to Elixir or run it from source, clone this repository
     $ cd elixir
     $ make clean test
 
+> Note: if you are running on Windows, [this article includes important notes for compiling Elixir from source on Windows](https://github.com/elixir-lang/elixir/wiki/Windows).
+
 If Elixir fails to build (specifically when pulling in a new version via git), be sure to remove any previous build artifacts by running `make clean`, then `make test`.
 
 If tests pass, you are ready to move on to the [Getting Started guide][1] or to try Interactive Elixir by running: `bin/iex` in your terminal.