In the future a plain "nimble install" for the Nim package manager
should work, but currently the initial git clone is necessary.
I have no idea if there is a change that that works on windows or
MacOSX, but at least for 64 bit Linux with GTK 3.22 chances are good
that install process works.
The git README already contains a small tutorial, but that is more for
Nim novices. People familiar with any GTK bindings or plain C GTK
should know how the Nim bindings can be used -- it may look a bit like