README.md update for darwin support

README.md

@@ -24,8 +24,12 @@ The editor can be customized by making changes to the
 [user module](data/user/init.lua).
 
 ## Building
-You can build the project yourself on Linux using the provided `build.sh`
-script. Note that the project does not need to be rebuilt if you are only making
+You can build the project yourself on *nix using the provided `build.sh`
+script.
+
+For Darwin / MacOS, assumes SDL2 available via `pkg-confing`. Packagers ought to provide this, so `brew install SDL2` should just work.
+
+Note that the project does not need to be rebuilt if you are only making
 changes to the Lua portion of the code.
 
 ## Contributing