Add Dockerfile and devcontainer

docs/docker.md

@@ -0,0 +1,16 @@
+# Docker Usage
+
+A prebuilt image containing Tor, OnionShare and the `voxvera` CLI is published to
+`ghcr.io/voxvera/voxvera`.
+
+```bash
+# pull the image
+docker pull ghcr.io/voxvera/voxvera:latest
+
+# run voxvera quickstart with flyers stored in ./flyers
+mkdir -p flyers
+docker run -it --rm -v "$(pwd)/flyers:/flyers" ghcr.io/voxvera/voxvera
+```
+
+The container uses `/flyers` as the working directory and runs `voxvera quickstart`
+by default. All generated flyer files will appear in the mounted `flyers` folder.