Bad link in Wiki to Schematic

[mrlinuxfish]

The PCB Wiki page has two links which point to a nonexistent Main branch instead of the Master branch. (both are links to the schematics).

Easiest solutions I see are:

• Renaming Master branch to Main
• Reformat the link to go to Master

I also decided to check all the other links in the wiki and noticed about half of the QMK links go to the beta docs and the other half to the main docs. In the past, the beta docs were identical, but better formatted, however, a while ago I had problems with the beta docs being out of date in relation to the main docs.