Fix remaining markdown formatting issues in the entire repository

[LKreutzer]

• Follow up to Apply linter autoformat to all documentation #14348
• Run markdown linter with autoformatter on the entire magma repository.
  • This was already done in docs: Format Markdown files in Magma #14827 and instructions can be found in the PR description.
  • Not all formatting errors could be automatically fixed by markdownlint.
• The files that are relevant are mainly readme files outside of the docs folder.
• Proposals and versioned docs should not be modified.
• Either:
  • wait and upgrade to a newer version of the tool or
  • manually go through the remaining issues or
  • find some other way of fixing the remaining markdown errors.