fix(op-overload): add notes

  int score;

  bool operator<(const student& a) const {

    return score < a.score || (score == a.score && name > a.name);

    // 上面省略了 this 指针，完整表达式如下：

    // this->score<a.score||(this->score==a.score&&this->name>a.name);

  }

};

priority_queue<student> pq;

};

bool operator<(const student& a, const student& b) {

  return a.score < b.score || (a.score == b.score && a.name > b.name);

  // 上面省略了 this 指针，完整表达式如下：

  // this->score<a.score||(this->score==a.score&&this->name>a.name);

}

priority_queue<student> pq;

```