add caddy config example

caddy/Dockerfile

@@ -0,0 +1,8 @@
+FROM caddy:builder AS builder
+
+RUN xcaddy build \
+    --with github.com/mholt/caddy-ratelimit \
+    --with github.com/caddy-dns/cloudflare
+FROM caddy:latest
+
+COPY --from=builder /usr/bin/caddy /usr/bin/caddy