updating README to clear up confusion on Rails 3 & 4

Author: potenza

README.md

@@ -8,26 +8,21 @@ integrate Twitter Bootstrap-style forms into your Rails App.
 ## Requirements
 
 * Ruby 1.9+
-* Rails 4.0+
+* Rails 3, 4
 * Twitter Bootstrap 2.0+
 
 ## Installation
 
 Add it to your Gemfile:
 
-### Rails 4.0+
-
 `gem 'bootstrap_form'`
 
-### Rails 3.1+
-
-`gem 'bootstrap_form', '~> 0.3.2'`
-
-
-Run the following command to install it:
+Then:
 
 `bundle`
 
+### Rails 3
+
 Add this line to app/assets/stylesheets/application.css.scss:
 
 ```css