fill-in build_system section

Signed-off-by: Michel-FK <michel.stempin@funkey-project.com>

docs/developer_guide/tutorials/build_system/compilation_environments.md

@@ -1,4 +1,107 @@
+Even if the resulting disk image and firmware update files are
+relatively small (202 MB and 55MB, respectively), the size of the
+corresponding sources and the compilation by-products tend to be
+rather large, such that an available disk space of at least 12GB is
+required during the build.
+
+And even if the resulting FunKey-OS boots in less than 5s, it still
+requires a considerable amount of time to compile: please account for
+1 1/2 hour on a modern multi-core CPU with SSD drives and a decent
+Internet bandwidth.
+
+The FunKey-OS is meant to be built on a native Ubuntu or Debian Linux
+host machine (Ubuntu 20.04 LTS in our case, but this should also work
+with other versions, too). And with only a few changes to the
+prerequisites, it can certainly be adapted to build on other common
+Linux distros.
+
+However, if your development machine does not match this setup, there
+are still several available solutions:
+
+ -  use a lightweight container system such as [Docker][1] and run an
+    Ubuntu or Debian Linux container in it
+
+ - use a VM (Virtual Machine), such as provided by [VirtualBox][2] and
+   run an Ubuntu or Debian Linux in it
+
+ - for Windows 10 users, use the [WSL2][3] (Windows System for Linux
+   2) subsystem and run an Ubuntu Linux distro in it
+
+In order to install one of these virtualized environments on your
+machine, please refer to the corresponding documentation.
+
+## Build on a Physical/Virtual Machine
+
+### Prerequisites
+
+While Buildroot itself will build most host packages it needs for the
+compilation, some standard Linux utilities are expected to be already
+installed on the host system. If not already present, you will need to
+install the following packages beforehand:
+
+ - bash
+ - bc
+ - binutils
+ - build-essential
+ - bzip2
+ - ca-certificates
+ - cpio
+ - cvs
+ - expect
+ - file
+ - g++
+ - gcc
+ - git
+ - gzip
+ - liblscp-dev
+ - libncurses5-dev
+ - locales
+ - make
+ - mercurial
+ - openssh-client
+ - patch
+ - perl
+ - procps
+ - python
+ - python-dev
+ - python3
+ - python3-dev
+ - python3-distutils
+ - python3-setuptools
+ - rsync
+ - rsync
+ - sed
+ - subversion
+ - sudo
+ - tar
+ - unzip
+ - wget
+ - which
+ - xxd
+
+On Ubuntu/Debian Linux, this is achieved by running the following
+command:
+
+```bash
+$ sudo apt install bash bc binutils build-essential bzip2 ca-certificates cpio cvs expect file g++ gcc git gzip liblscp-dev libncurses5-dev locales make mercurial openssh-client patch perl procps python python-dev python3 python3-dev python3-distutils python3-setuptools rsync rsync sed subversion sudo tar unzip wget which xxd
+```
+
+## Build in a Docker Container
+
+### Prerequisites
+
+When using a Docker container, all the prerequisites are automatically
+installed.
+
+## Build on Windows 10 with WSL2
+
+### Prerequisites
+
+
+[1]: https://www.docker.com/
+[2]:https://www.virtualbox.org/
+[3]: https://docs.microsoft.com/en-us/windows/wsl/install-win10
 
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