Small patch for DPI scaling issues

Hi!

Some users are having problems with the game's window starting way bigger than it should be. This is due to DPI scaling settings, and unfortunately right now I don't have a way of detecting whether a user has DPI scaling enabled or not.

Due to this I've added a hotkey (K) that decreases the window's size, and a message at the start telling the user to press this key if his window is too big. If your window size is normal then you can safely ignore it. Users who find themselves pressing this key can then go to the game's options (once you're in the arena) and click "fullscreen", which should scale the game's window to properly fit the screen.

If anyone has found any other bugs feel free to tell me about it. And I hope you're enjoying the game!