Update readme for 1.7.0

Author: BobbyMcWho

README.md

@@ -2,16 +2,14 @@
 
 [![Gem Version](http://img.shields.io/gem/v/omniauth-oauth2.svg)][gem]
 [![Build Status](http://img.shields.io/travis/omniauth/omniauth-oauth2.svg)][travis]
-[![Dependency Status](http://img.shields.io/gemnasium/omniauth/omniauth-oauth2.svg)][gemnasium]
-[![Code Climate](http://img.shields.io/codeclimate/github/intridea/omniauth-oauth2.svg)][codeclimate]
+[![Code Climate](http://img.shields.io/codeclimate/maintainability/intridea/omniauth-oauth2.svg)][codeclimate]
 [![Coverage Status](http://img.shields.io/coveralls/intridea/omniauth-oauth2.svg)][coveralls]
 [![Security](https://hakiri.io/github/omniauth/omniauth-oauth2/master.svg)](https://hakiri.io/github/omniauth/omniauth-oauth2/master)
 
 [gem]: https://rubygems.org/gems/omniauth-oauth2
 [travis]: http://travis-ci.org/omniauth/omniauth-oauth2
-[gemnasium]: https://gemnasium.com/github.com/omniauth/omniauth-oauth2
-[codeclimate]: https://codeclimate.com/github/omniauth/omniauth-oauth2
-[coveralls]: https://coveralls.io/r/omniauth/omniauth-oauth2
+[codeclimate]: https://codeclimate.com/github/intridea/omniauth-oauth2
+[coveralls]: https://coveralls.io/r/intridea/omniauth-oauth2
 
 This gem contains a generic OAuth2 strategy for OmniAuth. It is meant to serve
 as a building block strategy for other strategies and not to be used
@@ -34,6 +32,10 @@ module OmniAuth
       # This is where you pass the options you would pass when
       # initializing your consumer from the OAuth gem.
       option :client_options, {:site => "https://api.somesite.com"}
+      
+      # You may specify that your strategy should use PKCE by setting
+      # the pkce option to true: https://tools.ietf.org/html/rfc7636
+      option :pkce, true
 
       # These are called after authentication has succeeded. If
       # possible, you should try to set the UID without making
@@ -64,4 +66,3 @@ end
 ```
 
 That's pretty much it!
-