add json example

README.md

@@ -25,7 +25,15 @@ func main() {
 	rsHandler := roachslog.NewReachSlogHandler(handler)
 	slog.SetDefault(slog.New(rsHandler))
 
-	err := errors.New("error")
+  err := doSomething()
 	slog.Error("error occurred", roachslog.Err(err))
 }
+
+func doSomething() error {
+	return errors.New("error")
+}
+```
+
+```json
+{"time":"2024-09-06T12:44:15.107483+09:00","level":"ERROR","source":{"function":"main.main","file":"/Users/sdual/repos/golang/sample/main.go","line":22},"msg":"error occurred","error":"error","stacktrace":"\nmain.doSomething\n\t/Users/sdual/repos/golang/sample/main.go:26\nmain.main\n\t/Users/sdual/repos/golang/sample/main.go:21\nruntime.main\n\t/Users/sdual/go/1.22.4/pkg/mod/golang.org/[email protected]/src/runtime/proc.go:272\nruntime.goexit\n\t/Users/sdual/go/1.22.4/pkg/mod/golang.org/[email protected]/src/runtime/asm_arm64.s:1223"}
 ```