Set /workspace/development as default working dir

When one misses the part of the doc that says bench should be created under /workspace/development, bench is created in home directory and the work would be lost when the container is recreated. Making the directory default would avert that

.devcontainer/docker-compose.yml

@@ -23,6 +23,7 @@ services:
     command: sleep infinity
     volumes:
       - ..:/workspace:cached
+    working_dir: /workspace/development
     ports:
       - "8000:8000"
       - "9000:9000"