Add documentation for Twilio API
Add documentation for Twilio API

Closes #554

wheldom01/privacyidea,jh23453/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,jh23453/privacyidea,jh23453/privacyidea,privacyidea/privacyidea,jh23453/privacyidea,jh23453/privacyidea,wheldom01/privacyidea,wheldom01/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,wheldom01/privacyidea,wheldom01/privacyidea,jh23453/privacyidea,wheldom01/privacyidea