Restructured sample .env file, switched database to biarms/mysql

docker-compose.yml

@@ -22,7 +22,8 @@ x-environment:
 services:
   # MySQL Database
   mysql:
-    image: mysql:5.5
+    # The biarms/mysql Docker image supports ARM machines; you may also use mysql:5.5
+    image: biarms/mysql:5.5
     restart: on-failure
     environment:
       # Password for root access