feat(steam): further rich presence localization info

Steam/Readme.md

@@ -4,3 +4,39 @@
 This file is provided to Steam via Steamworks and used to create rich presence strings that show up in Steam for Resonite.
 
 While this file, resembles JSON, it is not actually JSON so please be careful, PRs are welcome!
+
+Valid languages are:
+English
+German
+French
+Italian
+Korean
+Spanish - Spain
+Simplified Chinese
+Traditional Chinese
+Russian
+Thai
+Japanese
+Portuguese - Portugal
+Polish
+Danish
+Dutch
+Finnish
+Norwegian
+Swedish
+Hungarian
+Czech
+Romanian
+Turkish
+Arabic
+Portuguese - Brazil
+Bulgarian
+Greek
+Ukrainian
+Spanish - Latin America
+Vietnamese
+Indonesian
+
+The language name is usually lowercased in the text file, but we can check for your after you PR the strings.
+
+see: https://partner.steamgames.com/doc/features/enhancedrichpresence#4 for more info.