Add warning when hiredis not installed. Recommend installation. (#1621)
Add warning when hiredis not installed. Recommend installation. (#1621)


andymccurdy/redis-py,alisaifee/redis-py,mozillazg/redis-py-doc,andymccurdy/redis-py,redis/redis-py,alisaifee/redis-py,redis/redis-py,mozillazg/redis-py-doc,andymccurdy/redis-py