Update README.md

refs: http:https://stackoverflow.com/questions/17157721/getting-a-docker-containers-ip-address-from-the-host/20686101#20686101

README.md

@@ -46,7 +46,7 @@ Our web container starts nginx, php5-fpm, redis, beanstalk. and has gruntjs, gul
 some relevant ports have been added to docker-compose.yml ( livereload standard port, karma server port ), change them if you need to.
 
 ### Notes
-- Use docker's local IP address to connect to your database, it's usually **172.17.0.1**, ``ifconfig`` in your terminal to make sure you got the correct IP address.
+- Use docker's local IP address to connect to your database. Run `docker inspect --format '{{ .NetworkSettings.IPAddress }}' ${CID}`, where `${CID}` is docker container ID of the database
 - Databases: by default mariadb is used as a database, but you are free to use any database you want: choose from these excellent images by Tutum: [tutum/mysql](https://github.com/tutumcloud/mysql) or [tutum/postgresql](https://github.com/tutumcloud/postgresql), they expose different environment variables, so don't forget to update your docker-compose file accordingly.