Updated broken RandR gamma comment.

src/x11_gamma.c

@@ -45,7 +45,8 @@ void _glfwInitGammaRamp(void)
 
         if (!sr->ncrtc || !XRRGetCrtcGammaSize(_glfw.x11.display, sr->crtcs[0]))
         {
-            // This is probably older Nvidia RandR with broken gamma support
+            // This is either a headless system or an older Nvidia binary driver
+            // with broken gamma support
             // Flag it as useless and fall back to Xf86VidMode, if available
             _glfwInputError(GLFW_PLATFORM_ERROR,
                             "X11: RandR gamma ramp support seems broken");