Add some doc for pch macro.
Add some doc for pch macro.
NicolasSchnitzler/dtk,rdebroiz/dtk,d-tk/dtk,d-tk/dtk,d-tk/dtk,d-tk/dtk,rdebroiz/dtk,d-tk/dtk,NicolasSchnitzler/dtk,rdebroiz/dtk,NicolasSchnitzler/dtk,rdebroiz/dtk,NicolasSchnitzler/dtk,d-tk/dtk