Update HeartbeatAlarmReceiver.java

app/src/main/java/com/nbee/echolink/broadcast/HeartbeatAlarmReceiver.java

@@ -33,6 +33,7 @@ public class HeartbeatAlarmReceiver extends BroadcastReceiver {
      */
     @Override
     public void onReceive(Context context, Intent intent) {
+        // 初始化上下文对象，为后续操作提供context
         thisContext = context;
         // 执行发送心跳信号的逻辑
         sendHeartbeatSignal();