Once you have obtained key.txt , setting it up with Cemu is relatively straightforward:
%USERPROFILE%\emudeck\EmulationStation-DE\Emulators\cemu . wii u keystxt for cemu
Cemu directory -> keys -> key.txt
Navigate to Android/data/info.cmu.cmu/files/ and paste it there. What Goes Inside keys.txt? Once you have obtained key