Update README with build instructions

README.md

@@ -2,9 +2,23 @@
 
 This is some code for querying/changing MacOS screen resolution that I
 found in multiple versions around the web.  It seemed useful, and as
-though it ought to be rescued, so I put it in a proper repository.
-Feel free to fork it and change it as you wish.  I am not supporting
-or maintaining this code, but if you find a compelling improvement, I
-might be inclined to accept your pull request ;-)
+though it ought to be rescued, so I put it in a proper repository and
+tried to reconstruct its revision history. 
+
+## Support/Maintenance
+
+I am not supporting or maintaining this code, but if you find a
+compelling improvement, I might be inclined to accept your pull
+request ;-)
+
+## Building
+
+This produces lots of warnings, but seems to work for me.
+
+```sh
+c++ setgetscreenres.m -framework ApplicationServices -o ~/bin/setgetscreenres -arch i386
+```
+
+## Enjoy!
 
 —Dave