Update guides/hack from HHVM repository

Author: Wilfred

guides/hack/40-contributing/01-introduction.md

@@ -72,14 +72,16 @@ automatically.
 
 ## Running An Old Instance
 
-If you want to see old versions of the docs, we provide [regular
-Docker images of this
-site](https://hub.docker.com/r/hhvm/user-documentation/tags). This is
-not suitable for development, but it's useful if you're working with
+If you want to see old versions of the docs, we provide [regular Docker
+images of this site](https://ghcr.io/hhvm/user-documentation) (previously
+on [Docker Hub](https://hub.docker.com/r/hhvm/user-documentation/tags)).
+This is not suitable for development, but is useful if you're working with
 an old HHVM/Hack version.
 
+
+
 1. Install [Docker](https://docs.docker.com/engine/installation/).
-2. Start a container with `docker run -p 8080:80 -d hhvm/user-documentation`.
+2. Start a container with: `docker run -p 8080:80 -d ghcr.io/hhvm/user-documentation`.
 3. You can then access a local copy of the documentation at <http://localhost:8080>.
 
 ## Running A Production Instance