docs: update README.md

README.md

@@ -27,7 +27,7 @@ rathole, like [frp](https://github.com/fatedier/frp) and [ngrok](https://github.
 
 ## Quickstart
 
-A full-powered `rathole` can be obtained from the [release](https://github.com/rapiz1/rathole/releases) page. Or [build from source](docs/build-guide.md) for other platforms and customizing the binary.
+A full-powered `rathole` can be obtained from the [release](https://github.com/rapiz1/rathole/releases) page. Or [build from source](docs/build-guide.md) for other platforms and customizing the binary. A [Docker image](https://hub.docker.com/r/rapiz1/rathole) is also available.
 
 The usage of `rathole` is ver similar to frp. If you have experience with the latter, then the configuration is very easy for you. The only difference is that configuration of a service is split into the client side and the server side, and a token is mandatory.