Add Docker/Compose hosting with Caddy 2 reverse-proxy docs

Serves the static index.html via a small nginx container and documents
pointing an existing Caddy 2 instance (local or remote) at it via FQDN
with automatic HTTPS.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PbwKCCj1vwAoqgRYDoqgeL

Dockerfile

@@ -0,0 +1,6 @@
+FROM nginx:1.27-alpine
+
+COPY index.html /usr/share/nginx/html/index.html
+COPY docker/nginx.conf /etc/nginx/conf.d/default.conf
+
+EXPOSE 80