Docs: say what the forge cannot render, and two headings by the style guide

The documentation sources are Zola Markdown: front matter between +++
lines, shortcodes that insert the example configurations, and @/ internal
links. A code forge shows all three unrendered, which the README used to
deny. A docs/README.md now explains each, and the README points to it.

"Configuring BGP Neighbors" becomes "BGP Neighbors", as the other feature
pages are titled; "When a Neighbor Restarts" becomes "Neighbor Restart", a
noun phrase as the style guide asks.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/README.md

@@ -0,0 +1,28 @@
+# Documentation sources
+
+This directory holds the sources of the Ferrix documentation site, built
+with [Zola](https://www.getzola.org):
+
+```bash
+zola --root docs serve     # http://127.0.0.1:1111, rebuilt on every change
+zola --root docs build     # into docs/public
+```
+
+The pages under `content/` are Markdown with Zola additions, which a code
+forge does not render:
+
+- The block between `+++` lines at the top of each page is its front
+  matter: the title, description and position in the navigation.
+- `{{ example(name="...") }}` and `{{ file(name="...") }}` insert a file
+  from [`examples/`](examples/), whole, at that point. Open the file to
+  read it.
+- Links of the form `@/docs/...` are internal links that Zola resolves and
+  checks at build time. On the forge they do not work; the target is the
+  path after `@/`, under `content/`.
+
+To read the documentation as intended, build the site, or read it where
+it is published (`base_url` in [`config.toml`](config.toml)).
+
+`STYLE.md` is the writing guide. CI builds the site on every push and fails
+on a link to a page or an anchor that does not exist; `zola --root docs
+check` also checks external links.