Well since the Trebuchet Launcher should be included with the ROM you already have installed (CM 11 M5) then you should have the choice whether to use it or Google Now Launcher, if you don't have this choice then maybe because the GApps package you installed is the (Full Stock Package) which by default replaces itself with any other launcher, my recommendation is to reinstall CM with different GApps package, you can browse different GApps packages from here.
Well since the Trebuchet Launcher should be included with the ROM you already have installed (CM 11 M5) then you should have the choice whether to use it or Google Now Launcher, if you don't have this choice then maybe because the GApps package you installed is the (Full Stock Package) which by default replaces itself with any other launcher, my recommendation is to reinstall CM with different GApps package, you can browse different GApps packages from here.
