service/documentation.md

@@ -644,6 +644,7 @@ Staff hours, hosting costs shadowed by GitLab.
    [geekdocs](https://geekdocs.de/) for a docs oriented theme
  * [ikiwiki][]: previously used, old, Perl, hard to setup, occult   templating system, slow
  * [lektor](https://www.getlektor.com/): used at Tor for other public websites
+ * [mdBook](https://rust-lang.github.io/mdBook/): useful to build user manuals, used by the Rust community
  * [Mkdocs](https://www.mkdocs.org/): also supported by [Read the docs](https://readthedocs.org/), similar to
    Sphinx, but uses Markdown instead of RST, [mike](https://github.com/jimporter/mike) can be used to
    support multiple versions in GitHub Pages