Update WordPress stack to use more environment variables so it's a better example

wordpress/stack.yml

@@ -8,10 +8,16 @@ services:
     ports:
       - 8080:80
     environment:
-      WORDPRESS_DB_PASSWORD: example
+      WORDPRESS_DB_HOST: db
+      WORDPRESS_DB_USER: exampleuser
+      WORDPRESS_DB_PASSWORD: examplepass
+      WORDPRESS_DB_NAME: exampledb
 
-  mysql:
+  db:
     image: mysql:5.7
     restart: always
     environment:
-      MYSQL_ROOT_PASSWORD: example
+      MYSQL_DATABASE: exampledb
+      MYSQL_USER: exampleuser
+      MYSQL_PASSWORD: examplepass
+      MYSQL_RANDOM_ROOT_PASSWORD: '1'