Improve linter output formatting for conda-forge.yml

[jaimergp]

Some notes [about the linter]:

• it doesn't tell which file this is all about
  • it could include a link to that exact file in the PR branch, such that a maintainer could click to edit
• as the output is for humans, it seems like rendering title, description, etc. as Markdown would be valuable.
  • however, as it was written (or dumped to) JSON Schema, it's would possible to generate a canonical link to the generated documentation for that schema item, once available
  • similarly, the raw repr that gets dumped could be a table
    • or, indeed, the whole thing could be a table
  • it may be worth putting these inside details tags

Now all we gotta do is schematize the other user-edited .yml :)

Originally posted by @bollwyvl in #1756 (comment)