docs: add Redis Pub/Sub LINK

Signed-off-by: Bo-Yi Wu <[email protected]>

Author: appleboy

README.md

@@ -4,7 +4,7 @@
 [![codecov](https://codecov.io/gh/golang-queue/redisdb/branch/main/graph/badge.svg?token=FFZN8E2ZZB)](https://codecov.io/gh/golang-queue/redisdb)
 [![Go Report Card](https://goreportcard.com/badge/github.com/golang-queue/redisdb)](https://goreportcard.com/report/github.com/golang-queue/redisdb)
 
-Redis as backend for [Queue package](https://github.com/golang-queue/queue)
+Redis [Pub/Sub](https://redis.io/docs/manual/pubsub/) as backend for [Queue package](https://github.com/golang-queue/queue)
 
 ## Setup