Docker: Re-add build block

If a user wants to build from source, let them. But the default
should fetch from the package registry.

Signed-off-by: kingbri <bdashore3@proton.me>

docker/docker-compose.yml

@@ -1,6 +1,12 @@
 version: '3.8'
 services:
   tabbyapi:
+    # Uncomment this to build a docker image from source
+    #build:
+    #  context: ..
+    #  dockerfile: ./docker/Dockerfile
+
+    # Comment this to build a docker image from source
     image: ghcr.io/theroyallab/tabbyapi:latest
     ports:
       - "5000:5000"