Add multiple shells section to Docker Hub docs

DOCKER_HUB.md

@@ -32,6 +32,37 @@ docker run -it --rm \
 
 Then run `opencode` when ready.
 
+## Running Multiple Shells
+
+Once opencode is running it takes over the terminal. To have a separate shell for `aws`, `git`, or other commands, run the container in the background and attach multiple times:
+
+```bash
+# Start in background
+docker run -d --name devbox \
+  -e ANTHROPIC_API_KEY=your-key \
+  -e OPENCODE_PROVIDER=anthropic \
+  -v ~/projects:/workspace \
+  -v ~/.ssh:/home/developer/.ssh:ro \
+  joakimp/opencode-devbox:latest sleep infinity
+
+# Shell 1: run opencode
+docker exec -it devbox opencode
+
+# Shell 2 (separate terminal): aws, git, etc.
+docker exec -it devbox bash
+
+# When done
+docker rm -f devbox
+```
+
+With docker-compose this is simpler:
+
+```bash
+docker compose up -d
+docker compose exec devbox opencode     # terminal 1
+docker compose exec devbox bash         # terminal 2
+```
+
 ## Environment Variables
 
 ### Provider Configuration