refine fly.io deployment guide

Author: cyyeh

packages/doc/docs/deployment/flydotio.mdx

@@ -176,4 +176,8 @@ Watch your app at https://fly.io/apps/xxxx/monitoring
 Visit your newly deployed app at https://xxxxx/
 ```
 
+:::info
+You can read more here regarding to [deployment via Dockerfile](https://fly.io/docs/languages-and-frameworks/dockerfile/).
+:::
+
 Congratulations! Now your VulcanSQL app is on the cloud and is ready to be shared to the world!