Update Readme.md

added test/example to get bearer/access_token from Twitter using consumer key+secret and OAuth2

Readme.md

@@ -13,6 +13,34 @@ Installation
     $ npm install oauth
 
 
+Examples
+==========
+
+```javascript
+describe('Trends',function(){
+  var request = require('superagent');
+  var OAuth = require('OAuth').OAuth;
+
+   it('gets bearer token', function(done){
+     var OAuth2 = require('OAuth').OAuth2;    
+     var twitterConsumerKey = 'your key';
+     var twitterConsumerSecret = 'your secret';
+     var oauth2 = new OAuth2(server.config.keys.twitter.consumerKey,
+       twitterConsumerSecret, 
+       'https://api.twitter.com/', 
+       null,
+       'oauth2/token', 
+       null);
+     oauth2.getOAuthAccessToken(
+       '',
+       {'grant_type':'client_credentials'},
+       function (e, access_token, refresh_token, results){
+       console.log('bearer: ',access_token);
+       done();
+     });
+   });
+```
+
 Change History
 ==============