Document tmpfs requirements

Author: AnastaZIuk

README.md

@@ -10,6 +10,11 @@ This repo is a Next.js app used to generate a static site. The final production
 - Runtime is static files only; mount/serve with RO filesystem (e.g., `docker run --read-only --tmpfs /tmp --tmpfs /config --tmpfs /data -p 3000:3000 www-website`).
 > ⚠️ The final container maps only the generated `out` directory and static assets; keep it read-only and do not run any Node/npm scripts there.
 
+## Runtime filesystem layout
+- The image is read-only, but Caddy still needs tiny writable slots for TLS cache/autosave/lock files.
+- Align tmpfs mounts with `docker-compose.yml`: `/tmp:size=32m`, `/config:size=16m`, `/data:size=16m`.
+- These small tmpfs allocations keep RAM usage predictable while allowing the static server to update its metadata safely.
+
 ## Deployment notes
 - Published image: `ghcr.io/devsh-graphics-programming/www-website` (tags: `latest`, `master`, `sha-*`).
 - Blog content is proxied separately; the main image does not include Node/npm or blog runtime.