Add a section about MarkDown

This commit adds a short documentation about Markdown/CommonMark and
tool recommendations.

README.md

@@ -139,3 +139,28 @@ git help switch
 
 If you would like to dive deeper into Git you can read the free [Pro Git
 book](https://www.git-scm.com/book/) on the Git website.
+
+## Markdown
+
+New documents should be written in Markdown syntax. Markdowns goal is to
+provide a human readable and writable syntax that can easily be transformed to
+representations in several output formats.
+
+We use the [CommonMark](https://commonmark.org/) variant of Markdown with the
+[table extension](https://github.github.com/gfm/#tables-extension-). CommonMark
+is well supported in Markdown libraries and conversion tools. The
+code.cacert.org system can render CommonMark Markdown documents to HTML
+allowing for easily accessible previews.
+
+### Recommended tooling
+
+To preview Markdown in several formats (HTML, PDF, Office documents) you can
+use [Pandoc](https://pandoc.org/) which is packaged for multiple Linux
+distributions and has installers for Windows and MacOS.
+
+As Markdown is a plain text format you may use any text editor like Vim,
+notepad++ and a lot of alternatives.
+
+If you prefer a live preview and some more assistance you may use a more
+heavyweight tool like Visual Studio Code or any of the JetBrains IDEs like
+PyCharm.