I started a page at https://wiki.geany.org/howtos/bsd/compiling
There's not much to it, as when I compiled geany on my BSD system there was nothing much I needed to do different from when I compile it on Linux.
I created it as a separate page under bsd/ as I figured that would allow for expansion of any specific BSD information in the future.
I'm pretty new to BSD, btw, so any other users familiar with BSD (cc @techee ) may want to review the page.