The easy, non-git way is just download the ones tagged as release https://github.com/godotengine/godot/releases
That if you want to work with stable, for using master and keep updating it, just do a pull from master repository (links are on the repo) and keep pulling updates (make a fork on your account if you intend to modify and push).
I do not know if kdevelop needs some special settings to compile and debug, it should not be different than qt creator.