How to project a coordinate system on an image?

Don’t know what links you followed but on the official GMT site you only have to follow the downloads tab.
But, specially on Windows, you only have to do ] add GMT and get everything. The wrapper and the lib.

Regarding the coordinates, I used a few from https://github.com/joa-quim/mirone/blob/master/data/wcity_major.dat but you can easily get them from GoogleEarth.