README - add port export for redis

Author: elpiel

README.md

@@ -39,7 +39,7 @@ We need two services to be able to run `Sentry`: `Postgres` and `Redis`.
 
 ### Running Redis
 
-`docker run --rm --name adex-validator-redis -d redis`
+`docker run --rm -p 6379:6379 --name adex-validator-redis -d redis`
 
 ### Running Sentry Rest API