feat: Add .norg support.

[tom-avilius]

.norg is a file type used by neorg.nvim to create notes as an alternative to markdown. So I guess supporting it could be straightforward.

And thankyou for this extension, it's great!

[elijah-potter]

I don't have time at the moment to get this dusted. It should be a straightforward application to Tree-sitter to get this working, if someone wants to pick it up.

See #79 and #353.