Update docker repo location in docs and docker-compose.yml

distrib/docker/docker-compose.yml

 
 services:
   ergo:
-    image: ergochat/ergo:latest
+    image: ghcr.io/ergochat/ergo:stable
     ports:
       - "6667:6667/tcp"
       - "6697:6697/tcp"

docs/MANUAL.md

 
 1. Pull the latest version of Ergo: `docker pull oragono/oragono:latest`
 1. Create a volume for persistent data: `docker volume create oragono-data`
-1. Run the container, exposing the default ports: `docker run -d --name oragono -v oragono-data:/ircd-data -p 6667:6667 -p 6697:6697 oragono/oragono:latest`
+1. Run the container, exposing the default ports: `docker run -d --name oragono -v oragono-data:/ircd-data -p 6667:6667 -p 6697:6697 ghcr.io/ergochat/ergo:stable`
 
 For further information and a sample docker-compose file see the separate [Docker documentation](https://github.com/oragono/oragono/blob/master/distrib/docker/README.md).