Bug 19179: Email option for SMSSendDriver is not documented

Bug 19179: Email option for SMSSendDriver is not documented

'Email' is not documented as a valid setting.

1) Apply patch.
2) Go to Administration --> search SMSSendDriver
3) Check if SMSSendDriver has this message is at the end of the box:
   "If you would prefer to receive SMS via E-mail set SMSSendDriver to Email"

Signed-off-by:  Michal Denar <black23@gmail.coml>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>