Document required module options in Kconfig for loading the vfb module.

diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index 6533b0f..6a68a43 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -1609,7 +1609,8 @@ config FB_VIRTUAL
 	  kernel option `video=vfb:'.
 
 	  To compile this driver as a module, choose M here: the
-	  module will be called vfb.
+	  module will be called vfb. In order to load it, you must use
+	  the vfb_enable=1 option.
 
 	  If unsure, say N.
 if VT