Docker: imagem do terminal e documentação de uso

Dockerfile em dois estágios (compila guara-cli e copia o binário para
debian-slim com smartmontools). Serve para hospedeiros Linux, servidores
sem desktop e arquivos de imagem forense. A interface gráfica fica de
fora de propósito: o guara ui só aceita 127.0.0.1.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RRZm8uTVN3WLTwcbrDQAUM

README.md

@@ -46,6 +46,8 @@ Every file has a `.sha256` next to it. To build from source: `cargo build --rele
 
 Reading raw disks requires privileges: **administrator** (Windows), `sudo` (Linux and macOS). Even as root, Guará writes sessions, reports and recovered files with the owner and permissions of the user who launched it.
 
+There is also a Docker image of the command line tool, for Linux hosts and for working on image files: see [docs/docker.md](docs/docker.md).
+
 ## Getting started
 
 ```bash