Fix MySQL docker command line in readme

readme.md

@@ -42,7 +42,7 @@ Note that whenever the database type is changed, the app needs to be run with a
 You could start MySql locally with whatever installer works for your OS, or with docker:
 
 ```
-docker run -e MYSQL_ROOT_PASSWORD=petclinic -e MYSQL_DATABASE=petclinic -p 3306:3306 mysql:5.7.8
+docker run -e MYSQL_USER=petclinic -e MYSQL_PASSWORD=petclinic -e MYSQL_ROOT_PASSWORD=root -e MYSQL_DATABASE=petclinic -p 3306:3306 mysql:5.7.8
 ```
 
 Further documentation is provided [here](https://github.com/spring-projects/spring-petclinic/blob/master/src/main/resources/db/mysql/petclinic_db_setup_mysql.txt).