Format *.md files with prettier

The `npm run format` command now matches
the husky `lint-staged`-commands.

Also upgraded to prettier v3.

prettier.config.js

@@ -2,4 +2,5 @@ module.exports = {
   tabWidth: 2,
   semi: true,
   singleQuote: true,
+  trailingComma: 'es5',
 };