Document basic_auth option

README.md

@@ -48,6 +48,7 @@ Next:
                    :save_to_file                   => Rails.root.join('pdfs', "#{filename}.pdf"),
                    :save_only                      => false,                        # depends on :save_to_file being set first
                    :proxy                          => 'TEXT',
+                   :basic_auth                     => false                         # when true username & password are automatically sent from session
                    :username                       => 'TEXT',
                    :password                       => 'TEXT',
                    :cover                          => 'URL',