[docs] testing guidelines

Signed-off-by: lizzie <lizzie@eden-emu.dev>

docs/user/README.md

@@ -35,6 +35,7 @@ A copy of this handbook is [available online](https://git.eden-emu.dev/eden-emu/
     - **[Obtainium](./ThirdParty.md#configuring-obtainium)**
     - **[ES-DE](./ThirdParty.md#configuring-es-de)**
     - **[Mirrors](./ThirdParty.md#mirrors)**
+    - **[GameMode](./ThirdParty.md#configuring-gamemode)**
 
 ## Advanced
 

docs/user/ThirdParty.md

@@ -66,3 +66,9 @@ Note: Even though the site isn't Codeberg, it uses the same Forgejo/Gitea backen
 ```xml
 <command label="Eden (Standalone)">%EMULATOR_EDEN% %ACTION%=android.nfc.action.TECH_DISCOVERED %DATA%=%ROMPROVIDER%</command>
 ```
+
+## Configuring GameMode
+
+There is a checkbox to enable gamemode automatically. The `libgamemode.so` library must be findable on the standard `LD_LIBRARY_PATH` otherwise it will not properly be enabled. If for whatever reason it doesn't work, see [Arch wiki: GameMode](https://wiki.archlinux.org/title/GameMode) for more info.
+
+You may launch the emulator directly via the wrapper `gamemode <program>`, and things should work out of the box.