Clarify API versions that support Audio Forwarding

Reword the supported API versions for audio forwarding sentence to
clarify that it supports API >= 30

PR #3949 <https://github.com/Genymobile/scrcpy/pull/3949>

Signed-off-by: Romain Vimont <rom@rom1v.com>

README.md

@@ -39,7 +39,7 @@ Its features include:
 
 The Android device requires at least API 21 (Android 5.0).
 
-[Audio forwarding](doc/audio.md) is supported from API 30 (Android 11).
+[Audio forwarding](doc/audio.md) is supported for API >= 30 (Android 11+).
 
 Make sure you [enabled USB debugging][enable-adb] on your device(s).