Updated RGUI (markdown)

RGUI.md

@@ -34,8 +34,19 @@ it can do the most common things you would want to do while using RetroArch.
 - Mute/unmute audio
 - Exit RetroArch (yes, sadly :p)
 
+## Config file
+By default, RetroArch looks for a config in various places depending on OS:
+
+- **Linux/OSX**: `$XDG_CONFIG_HOME/retroarch/retroarch.cfg`, then `~/.config/retroarch/retroarch.cfg`, then `~/.retroarch.cfg`, and finally, as a fallback, `/etc/retroarch.cfg`.
+- **Windows**: `retroarch.cfg` in same folder as `retroarch.exe`, then `%APPDATA%\retroarch.cfg`.
+
+To override this, use `retroarch --config customconfig.cfg`. If you have some special options you want to store in separate config files you can use `retroarch --config baseconfig.cfg --appendconfig specialconfig.cfg`. See man-page and/or `--help` for detail.
+
+### Warning
 While you are changing settings in runtime, they are not saved to disk afterwards on PC.
-By design, the config file is considered immutable as it is likely maintained by the user.
+By design, the config file is considered immutable as it is likely maintained by the user,
+and should not be overwritten behind the users back. This is not the case on consoles however, where
+looking at the config manually isn't really an option for most users.
 
 ## Entering the menu