chore: Add more linters

[bradenhilton]

This might not work right away...

[bradenhilton]

For info, if this is merged and works well, we could consider also using it for chezmoi, given that the repo contains Go/Markdown/Python/PowerShell/Shell/YAML/etc. files.

[twpayne]

I'd rather configure individual linters than use MegaLinter. Reasons:

• We can update individual linters more easily, instead of having to wait for MegaLinter bulk updates. It's easier to stay on top of multiple small changes than a few, occasional large ones.
• Totally subjective, but MegaLinter is just so terribly ugly. Its config files, its output, its interface... It makes my eyes hurt.
• Biased, but I don't want to have to install NodeJS on any of my systems due to npm hell and NodeJS regularly breaking backwards compatibility.

[bradenhilton]

@twpayne Valid points. Would you prefer if rework this PR to use individual linters?

The markdown linter is there because I have some (rough) initial documentation ready.

[twpayne]

Would you prefer if rework this PR to use individual linters?

Yes please!

Also, please consider adding the Markdown linters to twpayne/chezmoi.

[twpayne]

Thank you!