Add `redis.sentinel.Sentinel` module documentation (#1165)
Add `redis.sentinel.Sentinel` module documentation (#1165)

Added directive to document Sentinel module.
alisaifee/redis-py,5977862/redis-py,andymccurdy/redis-py,mozillazg/redis-py-doc,andymccurdy/redis-py,mozillazg/redis-py-doc,redis/redis-py,alisaifee/redis-py,andymccurdy/redis-py,5977862/redis-py,5977862/redis-py,redis/redis-py