Update to Readme for 3-legged authorization

fixes issue #81

Author: gouthamvel

README.rdoc

@@ -47,6 +47,8 @@ When user returns create an access_token
   hash = { oauth_token: session[:token], oauth_token_secret: session[:token_secret]}
   request_token  = OAuth::RequestToken.from_hash(@consumer, hash)
   @access_token = @request_token.get_access_token
+  # For 3-legged authorization, flow oauth_verifier is passed as param in callback
+  # @access_token = @request_token.get_access_token(oauth_verifier: params[:oauth_verifier]) 
   @photos = @access_token.get('/photos.xml')
 
 Now that you have an access token, you can use Typhoeus to interact with the OAuth provider if you choose.