Don't remove trailing whitespace from markdown

[Bananeweizen]

2 blanks at the end of a line render as linebreak, without starting a new paragraph. Therefore markdown file rendering would change when removing all trailing whitespace.

I haven't found any normative reference for that, but rather learned this from a colleague today. And that VS Code also did it wrong in the past: https://github.com/microsoft/vscode/issues/1679