Update build instructions

#849

README.md

@@ -126,6 +126,8 @@ If you wish to run a development build of Twinkly Tray:
 - Run `npm install`.
 - Run `npm run build` to build an executable or `npm start` to run a development build.
 
+*Note: Twinkle Tray must be built on Windows.*
+
 ## Special Thanks
 
 Twinkle Tray was built using frameworks & libraries such as [Electron](https://electronjs.org/), [Node.js](https://nodejs.org/), [node-ddcci](https://github.com/hensm/node-ddcci), and [win32-displayconfig](<https://github.com/djsweet/win32-displayconfig>). Thanks to Weblate for allowing free use of their service, along with the many contributors to the localizations of Twinkle Tray. The app would not be nearly as popular without all of your help. And thank you for the many donations, small and large, over the years.