Update README to mention ruby version management tools

README.md

@@ -26,6 +26,8 @@ following command:

    $ git clone https://github.com/mruby/mruby.git

You can also install and compile mruby using [ruby-install](https://github.com/postmodern/ruby-install), [ruby-build](https://github.com/rbenv/ruby-build) or [rvm](https://github.com/rvm/rvm).

## mruby home-page

The URL of the mruby home-page is: [http://www.mruby.org](http://www.mruby.org).