Fixed broken links to Trenchbroom's Setup Guide

[mynameiswhm]

I've fixed two broken links to setup guide which were using domain name without protocol (resulting in invalid link in the final rendered page: https://qodotplugin.github.io/docs/beginner's-guide-to-qodot/qodotplugin.github.io/docs/beginner's-guide-to-qodot/trenchbroom-setup.html). There's also one working hardcoded link to beginner's guide.

I've changed those links to relative markdown files (which should be converted by markdown renderer, just like in other parts of the docs).

[mynameiswhm]

There's also #17 which fixes the same problem, but I think using relative markdown links and relying on documentation renderer to use them is a preferred way, rather than hardcoding public URL.