Command syntax is wrong in README

[eddiebeltran33]

This is the README command:
docker-compose up -f docker-compose.mysql.yml -d
This is what it must say (at least on docker-compose 1.21+)
docker-compose -f docker-compose.mysql.yml up -d

[Dmitry Khomutov]

@eddiebeltran33 Thanks. Can you create pull request with fix?