Update README.md (#2379)

Default now uses Turbo instead of Small

README.md

@@ -85,7 +85,7 @@ The following command will transcribe speech in audio files, using the `turbo` m
 
     whisper audio.flac audio.mp3 audio.wav --model turbo
 
-The default setting (which selects the `small` model) works well for transcribing English. To transcribe an audio file containing non-English speech, you can specify the language using the `--language` option:
+The default setting (which selects the `turbo` model) works well for transcribing English. To transcribe an audio file containing non-English speech, you can specify the language using the `--language` option:
 
     whisper japanese.wav --language Japanese