Provide multi-platform docker builds. Closes #119.

README.md

@@ -117,6 +117,8 @@ Alternatively, if you have already cloned the repo, you can fetch just the prebu
 
 > **Warning:** Docker has had reports intermittent issues with serial event subscriptions. The native method above is more reliable.
 
+Local Docker builds are architecture-native by default. On Apple Silicon Macs and ARM64 Linux hosts such as Raspberry Pi, `docker compose build` / `docker compose up --build` will produce an ARM64 image unless you override the platform.
+
 Edit `docker-compose.yaml` to set a serial device for passthrough, or uncomment your transport (serial or TCP). Then:
 
 ```bash
@@ -148,6 +150,15 @@ docker compose pull
 docker compose up -d
 ```
 
+Published Docker tags are intended to be multi-arch (`linux/amd64` and `linux/arm64`). If you are building and publishing manually, use Docker Buildx:
+
+```bash
+docker buildx build \
+  --platform linux/amd64,linux/arm64 \
+  -t jkingsman/remoteterm-meshcore:latest \
+  --push .
+```
+
 The container runs as root by default for maximum serial passthrough compatibility across host setups. On Linux, if you switch between native and Docker runs, `./data` can end up root-owned. If you do not need that serial compatibility behavior, you can enable the optional `user: "${UID:-1000}:${GID:-1000}"` line in `docker-compose.yaml` to keep ownership aligned with your host user.
 
 To stop: