Add important note about brightness on OS X

keyboard/ergodox_ez/keymaps/romanzolotarev-norman-plover-osx/readme.md

@@ -30,6 +30,10 @@ There are four layers:
 - Tap `F3`, `F4`, `F5`, `F6` to resize a window via [Divvy](http://mizage.com/divvy/).
 - Tap `F14`, `F15` to adjust display brightness. 
 
+**IMPORTANT**: If you have another keyboard connected via Bluetooth, then `F14` and `F15` will not work.
+Turn off that Bluetooth keyboard. Re-plug you ErgoDox. Enjoy!
+
+
 ## CTRL/ESC
 
 Both of those keys are frequently used in Vim.