Fix: Update bind-mount image

This command will fail, as there is no existing app directory in the alpine image. We must provide the app image `getting-started` or the image from your Docker hub.

docs/tutorial/using-bind-mounts/index.md

@@ -41,7 +41,7 @@ So, let's do it!
     ```bash
     docker run -dp 3000:3000 \
         -w /app -v ${PWD}:/app \
-        node:12-alpine \
+        getting-started \
         sh -c "yarn install && yarn run dev"
     ```