feat(code-server): mount the host docker socket

Bind-mount /var/run/docker.sock so the universal-docker mod's CLI has a
daemon to talk to, and document the sibling-container and permission
caveats in the service README.

code-server/compose.yml

@@ -19,5 +19,6 @@ services:
       - GIT_COMMITTER_EMAIL=${GIT_EMAIL}
     volumes:
       - 'code-server-config:/config'
+      - '/var/run/docker.sock:/var/run/docker.sock'
 volumes:
   code-server-config: