Restructure of the docs content

docs/developer/buildsystem/gh-pages.md

@@ -0,0 +1,52 @@
+---
+parent: Build system
+grand_parent: Developer
+nav_order: 3
+---
+
+# Build GitHub Pages
+
+This documentation is created by [GitHub Pages]. The source files are
+stored in the repository [MOOSE] in the subfolder `docs`.
+We use [Just the Docs], which is a modern, highly customizable, and responsive
+[Jekyll] theme for documentation.
+
+{: .note }
+> The class documentation is created by its own [build] and is not the scope for this page!
+
+The build steps to create this documentation are defined in [.github/workflows/gh-pages.yml].
+
+It is divided into two jobs:
+- build:
+    - Only changes to in the subfolder `docs` or `gh-pages.yml` will trigger a build.
+    - Checkout of the git repository [MOOSE].
+    - Setup [Ruby] version 3.1, which is needed by [Jekyll].
+    - Run action [configure-pages].
+    - Build with [Jekyll].
+    - Run action [upload-pages-artifact].
+- deploy:
+    - Run action [deploy-pages].
+
+# Preview of this documentation
+
+When enhancing this documentation it is very useful to see a 1on1 preview of the pages.
+This can be displayed as follows:
+
+- You need a working installation of [Docker].
+- Go to the `docs` subfolder.
+- Run `docker compose up`.
+- Open a browser with the following URL: `http://127.0.0.1:4000/`.
+- After a change of the [Markdown] files, wait some seconds and press F5 in the browser.
+
+[GitHub Pages]: https://pages.github.com/
+[MOOSE]: https://github.com/FlightControl-Master/MOOSE
+[Just the Docs]: https://github.com/just-the-docs/just-the-docs
+[Jekyll]: https://jekyllrb.com/
+[Ruby]: https://www.ruby-lang.org/en/
+[build]: build-docs.md
+[.github/workflows/gh-pages.yml]: https://github.com/FlightControl-Master/MOOSE/blob/master/.github/workflows/gh-pages.yml
+[configure-pages]: https://github.com/actions/configure-pages/
+[upload-pages-artifact]: https://github.com/actions/upload-pages-artifact
+[deploy-pages]: https://github.com/actions/deploy-pages/
+[Docker]: https://www.docker.com/
+[Markdown]: https://www.markdownguide.org/