doc key_config file location on windows

Author: Stephan Dilly

KEY_CONFIG.md

@@ -12,5 +12,6 @@ The location of the file depends on your OS:
 * `$HOME/.config/gitui/key_config.ron` (mac)
 * `$XDG_CONFIG_HOME/gitui/key_config.ron` (linux using XDG)
 * `$HOME/.config/gitui/key_config.ron` (linux)
+* `%APPDATA%/gitui/key_config.ron` (Windows)
 
 Here is a [vim style key config](vim_style_key_config.ron) with `h`, `j`, `k`, `l` to navigate. Use it to copy the content into `key_config.ron` to get vim style key bindings.