Even still in development i like the grav and sure the gantry documentation.
What is still missing and in my mind compulsory and required is a documentation or at least a COOKBOOK for the usage of the COMBINATION of Grav and Gantry.
The specific documentation about grav or gantry does not answer the questions about concepts to get the things done from the combined point of view.
Contents could be interaction, relation, examples of concepts, proven concepts, best practices, why grav with gantry, etc..
I think this is necessary to point us in the direction which the rockettheme brains intended to. Maybe more for newbies but also for profis.
Gantry is CMS agnostic... it works the same way regardless of the underlying CMS... in that, I feel the docs.gantry.org documentation is already very robust... are there any specific questions you have at this point?
All of the Grav and Gantry documentation is hosted on GitHub. If you feel it could be improved or have something you want to edit or contribute I'd definitely recommend posting on and contributing to those repos: