3.x video notes

Things I maybe should have mentioned to note for the future:

* I don't need to split latitude and longitude string since it stays as comma-delimited for both dark sky and openAQ!
* I should have been more specific once I start using URL query string with openAQ and tied that back to how I'm doing the GET request with URL parameters in my node server.

此说明中没有指定文件、测试或具体的代码更改。首先查看视频材料以及涉及 OpenAQ、URL 查询字符串和 GET 参数的 Node 服务器示例；要视为完成，必须就更新这些说明的范围达成一致。

由索引模型根据 Issue 内容生成。