add description for echo server

serveCommand.go

 	switch in.body.(type) {
 	case TextMsg:
 		m := in.body.(TextMsg)
-		str, err = BuildTextMsg(openID, m.Content+"\n\n 转接 可以测试客服")
+		str, err = BuildTextMsg(openID, m.Content+"\n\n关键词 [转接] 将后续信息都转接到 客服")
 		if m.Content == "转接" {
 			processed = false
 		}