Turn README into MarkDown README.md

[basxto]

I redid #42

Tested with:

• github (anchor link works)
• my gitea instance at home (anchor link works)
• less README.md
• mdcat -p README.md
• cmark README.md > /tmp/readme.html && lynx /tmp/readme.html
• pandoc --metadata title="Mark Tyler's Painting Program" --standalone -o /tmp/readme.html README.md && lynx /tmp/readme.html (anchor link works)