Fix code examples in voice pipeline quickstart docs (#277)

Author: rm-openai

docs/voice/quickstart.md

@@ -100,10 +100,13 @@ pipeline = VoicePipeline(workflow=SingleAgentVoiceWorkflow(agent))
 ```python
 import numpy as np
 import sounddevice as sd
+from agents.voice import AudioInput
 
 # For simplicity, we'll just create 3 seconds of silence
 # In reality, you'd get microphone data
 audio = np.zeros(24000 * 3, dtype=np.int16)
+audio_input = AudioInput(buffer=buffer)
+
 result = await pipeline.run(audio_input)
 
 # Create an audio player using `sounddevice`