Add link validator and Linting

Created by: maxwolfs

closes #18 (closed)

This PR is

• adding a link validator action that checks on every PR if there are broken links within markdown files.
• enforcing pre commit checking and linting of markdown files using markdownlint with prettier, husky and lint-staged
• adding a markdownlint action that checks on every PR if all committed markdown comply to the markdown rules

The guide i still a first shot and needs further explanation how to set it up easily on other repositories