chore: update env local example with redis_url

.env.local.example

@@ -7,3 +7,6 @@ NEXT_PUBLIC_URL=
 # AXIOS_USERAGENT=
 # default accept header is 'application/json, text/plain, */*'
 # AXIOS_ACCEPT=
+
+# for docker, just set the domain to the container name, default is 'libremdb_redis'
+REDIS_URL=localhost:6379