Fix GH-Actions Markdown Lint Checker

[rossgalloway]

The Markdown lint checker that runs automatically on all PRs to check for broken links usually fails and reports broken links where they do not exist.

• Image links throw errors but work on build: [✖] /img/DAO/here-we-are-cropped.jpg → Status: 400
• Relative links to other pages throw status: 400 errors but work fine. [✖] ../getting-started/intro → Status: 400
• Some sites get status: 403 errors but work fine: [✖] https://www.reddit.com/r/yearn_finance/ → Status: 403
• Status: 404 errors are usually correctly marked as not found
• Status: 0 are usually correctly marked as not existing.