Replace mrtest wiki page with the new documentation

Thanks to the extraordinary work done by @longnoserob we know have a great documentation page: https://docs.postmarketos.org/mrhlpr/ However, how to actually use mrtest is still on the wiki: https://wiki.postmarketos.org/wiki/Mrtest It would be ideal, if we could replace that wiki page with proper documentation in code here, for example, in https://docs.postmarketos.org/mrhlpr/usage.html#mrtest We would also need to find links to that webpage (like the testing team in the wiki and replace them