add forwarded ports for browser-sync

.devcontainer/docker-compose.yml

@@ -17,6 +17,10 @@ services:
       context: .
       dockerfile: Dockerfile
 
+    ports:
+      - 3000:3000
+      - 3001:3001 # for browser-sync
+
     volumes:
       - ..:/workspace/growi:cached
       - /workspace/growi/node_modules