Gaming: Added optional accotation to changing Proton's log directory

Author: Shendisx

src/content/docs/configuration/gaming.mdx

@@ -334,7 +334,7 @@ To enable Proton logging for a game:
         This will create a log file in your home directory, named `steam-<AppID>.log` (for example, Counter Strike 2 uses AppID **730**, so the file would be `steam-730.log`).
 </Steps>
 
-* To set a custom log directory, use `PROTON_LOG_DIR`
+* **(Optional)** To set a custom log directory, use `PROTON_LOG_DIR`
 
 ```bash title='Example'
 PROTON_LOG=1 PROTON_LOG_DIR=/home/cachyos/steam-logs %command%