Fix missing database user for Wordpress service (docker#2824)

* Fix missing database user for Wordpress service

It defaults to root if not specified. https://hub.docker.com/_/wordpress/

* Change root password to avoid confusion.

compose/wordpress.md

@@ -40,7 +40,7 @@ Compose to set up and run WordPress. Before starting, you'll need to have
            - db_data:/var/lib/mysql
          restart: always
          environment:
-           MYSQL_ROOT_PASSWORD: wordpress
+           MYSQL_ROOT_PASSWORD: somewordpress
            MYSQL_DATABASE: wordpress
            MYSQL_USER: wordpress
            MYSQL_PASSWORD: wordpress
@@ -54,6 +54,7 @@ Compose to set up and run WordPress. Before starting, you'll need to have
          restart: always
          environment:
            WORDPRESS_DB_HOST: db:3306
+           WORDPRESS_DB_USER: wordpress
            WORDPRESS_DB_PASSWORD: wordpress
     volumes:
         db_data: