Restructure of the docs content

docs/developer/buildsystem/index.md

@@ -0,0 +1,61 @@
+---
+layout: default
+title: Build system
+parent: Developer
+has_children: true
+nav_order: 99
+---
+
+# Build system
+
+{: .note }
+> This documentation is not needed for end users. Only the people of the
+> development team, who must maintain the build system need to read this.
+
+In this document we want to describe our build system for MOOSE.
+MOOSE consists of multiple [Lua] files. Each class is stored in its own file.
+This is needed for MOOSE developers to maintain clarity.
+For users this is not practical, because they want to include the whole framework
+as a single file into their missions.
+
+Because of this the build will collect all needed files and merge them together
+in one file with the name `Moose.lua`. It includes also all comments and the
+class documentation. Because of this its size is about 6-7 MB.
+
+To reduce the size of the file and make mission files smaller, the Moose team
+decided to create a version without all comments and documentation. This file
+is named `Moose_.lua`. It is created by a tool with the name [LuaSrcDiet].
+
+Both files will be called static includes. In other programming languages includes
+are dependencies. For Moose it is easier to memorize, that these files must be
+included in your mission to use Moose. It is an static approach because you need
+to add it once and it is only read from inside of the mission file after that.
+A dynamic approach is to load all the single class files on each mission start
+from the hard disk. But this is more for advanced Moose users and Moose developers.
+
+## Details
+
+In the past [AppVeyor] was used to run the build on a Windows system.
+We decided to migrate this build to [GitHub Actions]. Installation of
+dependencies was not stable on Windows with [GitHub Actions]. So we switched
+to Ubuntu Linux.
+
+### GitHub Actions yml files
+
+The build configuration is stored in the folder `.github/workflows`. You will find
+multiple files in this directory:
+
+- [build-docs.yml] - Job definition to generate the class documentation
+- [build-includes.yml] - Job definition to build the static includes
+- [gh-pages.yml] - Job to build this documentation page
+
+We decided to use different files for each job for separation of duties and easier
+maintenance.
+
+[Lua]: https://www.lua.org/
+[LuaSrcDiet]: https://github.com/jirutka/luasrcdiet
+[AppVeyor]: https://www.appveyor.com/
+[GitHub Actions]: https://docs.github.com/en/actions
+[build-docs.yml]: build-docs.md
+[build-includes.yml]: build-includes.md
+[gh-pages.yml]: gh-pages.md