Document usage

README.md

@@ -1,6 +1,24 @@
 # Middleman Build Pack
 
-This is a build pack for [Middleman](http://middlemanapp.com) that is
-intended to be used with [heroku-buildpack-multi](https://github.com/ddollar/heroku-buildpack-multi).
-It will create your middleman static site assuming your Ruby dependencies
-are already met.
+This is a build pack for [Middleman](http://middlemanapp.com) that will
+create your static site.
+
+It is cleaner than most Middleman build packs out there because it
+takes advantage of the [heroku-buildpack-multi](https://github.com/ddollar/heroku-buildpack-multi)
+buildpack to separate out the Ruby and Middleman specific components.
+
+## Usage
+
+This build pack is meant to be used with the
+[heroku-buildpack-multi](https://github.com/ddollar/heroku-buildpack-multi)
+buildpack. Setup generally goes like this with an existing Heroku app:
+
+```
+$ heroku config:add BUILDPACK_URL=https://github.com/ddollar/heroku-buildpack-multi.git
+...
+$ cat .buildpacks
+https://github.com/heroku/heroku-buildpack-ruby.git
+https://github.com/hashicorp/heroku-buildpack-middleman.git
+```
+
+Then just push!