Add dependent packages for Debian/Ubuntu

README.rdoc

@@ -27,7 +27,7 @@ FXRuby supportes everything of FOX, that is useful in Ruby:
 
 FXRuby runs on Linux, Windows and OS-X. Installation on *nix requires
 FOX development headers and libraries installed:
-* on Debian/Ubuntu: <tt>sudo apt-get install libfox-1.6-dev</tt>
+* on Debian/Ubuntu: <tt>sudo apt-get install g++ libxrandr-dev libfox-1.6-dev</tt>
 * see also detailed installation instructions in the {https://github.com/lylejohnson/fxruby/wiki Wiki}
 * no preparation needed on Windows - the binary gem can be used