docs: update

Author: WqyJh

README.md

@@ -2,7 +2,7 @@
 
 [![Go Reference](https://pkg.go.dev/badge/github.com/WqyJh/go-openai-realtime.svg)](https://pkg.go.dev/github.com/WqyJh/go-openai-realtime)
 [![Go Report Card](https://goreportcard.com/badge/github.com/WqyJh/go-openai-realtime)](https://goreportcard.com/report/github.com/WqyJh/go-openai-realtime)
-[![codecov](https://codecov.io/gh/WqyJh/go-openai-realtime/branch/master/graph/badge.svg?token=bCbIfHLIsW)](https://codecov.io/gh/WqyJh/go-openai-realtime)
+[![codecov](https://codecov.io/gh/WqyJh/go-openai-realtime/branch/main/graph/badge.svg?token=bCbIfHLIsW)](https://codecov.io/gh/WqyJh/go-openai-realtime)
 
 This library provides unofficial Go clients for [OpenAI Realtime API](https://platform.openai.com/docs/api-reference/realtime). We support all 9 client events and 28 server events.