Marker docker section as BETA

(Here be dragons)

README.md

@@ -54,7 +54,7 @@ Some platforms/distros also have Oragono packages maintained for them:
 
 * Arch Linux [AUR](https://aur.archlinux.org/packages/oragono/) - Maintained by [Sean Enck (@enckse)](https://github.com/enckse).
 
-### Using Docker
+### Using Docker (BETA)
 
 A Dockerfile and docker-compose recipe are available in the [oragono-docker](https://github.com/oragono/oragono-docker) repository.