Emby API Key Update

Added note to the Emby Plugin Documentation

docs/plugins/embyupdate.rst

@@ -9,6 +9,7 @@ To use ``embyupdate`` plugin, enable it in your configuration (see :ref:`using-p
         host: localhost
         port: 8096
         username: user
+        apikey: apikey
         password: password
 
 To use the ``embyupdate`` plugin you need to install the `requests`_ library with::
@@ -30,4 +31,5 @@ The available options under the ``emby:`` section are:
 - **port**: The Emby server port.
   Default: 8096
 - **username**: A username of a Emby user that is allowed to refresh the library.
-- **password**: That user's password.
+- **apikey**: An Emby API key
+- **password**: If no API key is present then enter the user aboves password.