Replace Bundler instruction with gem-install instruction.

README.rdoc

@@ -3,8 +3,6 @@
 {<img src="https://secure.travis-ci.org/songkick/oauth2-provider.png?branch=master" alt="Build Status" />}[http://travis-ci.org/songkick/oauth2-provider]
 {<img src="https://codeclimate.com/badge.png" />}[https://codeclimate.com/github/songkick/oauth2-provider]
 
-  gem 'songkick-oauth2-provider'
-
 This gem provides a toolkit for adding OAuth2 provider capabilities to a Ruby
 web app. It handles most of the protocol for you: it is designed to provide
 a sufficient level of abstraction that it can implement updates to the protocol
@@ -19,6 +17,11 @@ framework-specific request objects, though you can pass those in and their
 It stores the clients and authorizations using ActiveRecord.
 
 
+=== Installation
+
+  gem install songkick-oauth2-provider
+
+
 === A note on versioning
 
 This library is based on draft-10[http://tools.ietf.org/html/draft-ietf-oauth-v2-10],