To include new lyrics providers, it's added here:
https://github.com/strawberrymusicplayer/strawberry/blob/master/src/core/application.cpp#L68
and:
https://github.com/strawberrymusicplayer/strawberry/blob/master/src/core/application.cpp#L155

Then here: https://github.com/strawberrymusicplayer/strawberry/blob/master/src/CMakeLists.txt#L162
and here: https://github.com/strawberrymusicplayer/strawberry/blob/master/src/CMakeLists.txt#L378