specify working_dir in docker-compose.yml

- simplifies discovery of mounted directory for docker-compose users

docker-compose.yml

@@ -24,6 +24,7 @@ services:
     - .:/mnt/io
     tty: true
     shm_size: '1gb'
+    working_dir: /mnt/io
   dev-complex:
     build:
       args:
@@ -32,5 +33,6 @@ services:
       dockerfile: Dockerfile
     volumes:
     - .:/mnt/io
+    working_dir: /mnt/io
     tty: true
     shm_size: '1gb'