RQDA/RGtk2 Installation Problem

Greetings,

I have been having a problem installing RQDA on my Mac (OS 10.13.2). I
followed the installation process on the RQDA page (http://rqda.r-forge.r-
project.org/), but I keep getting an error message saying that I am missing
pkg-config and GTK. I reinstalled XQuartz and GTK+ 2.24.17 multiple times
(and reinstalled R version 3.4.4), but kept receiving the same error
message.

Some kind person suggested this page as a possible solution:

https://stackoverflow.com/questions/19645590/running-
rattle-on-mac-os-x-10-9-mavericks/19719518#19719518

I am stuck after "brew install gtk+ cairo." I have very little knowledge of
coding, and unsure how to create or modify  ~/.R/Makevars....

My apologies for a noob question, but would appreciate if you could walk me
through, or point me to a step-by-step tutorial, if it is available. I have
already installed XCode and Command Line Tools.

Thank you in advance for your help.

Ryoko