fix: docs Pages deploy permissions and document GitHub Pages setup

Deploy job failed because Pages source must be GitHub Actions; document
About/description guidance and fix workflow job permissions.

docs-site/en/guide/local-dev.md

@@ -52,3 +52,15 @@ npm run docs:preview
 ```
 
 Sources live in `docs-site/`; screenshot sources are in `docs/screenshots/` (including `login.png`), copied to `docs-site/public/screenshots/` before build.
+
+## Publish to GitHub Pages
+
+Live docs: <https://o96u.github.io/PicHost/>
+
+**First-time setup** (if deploy fails or the site 404s):
+
+1. Repo **Settings → Pages**
+2. **Build and deployment → Source** → **GitHub Actions** (not “Deploy from a branch”)
+3. Push to `main` or run the `docs` workflow manually from Actions
+
+Allow 1–2 minutes after a successful deploy. If the `deploy` job fails immediately, Pages is usually not enabled yet.