winform chart控件单点标注

没实现

参考链接（前三条有点跑题，但我也许能用上）：
https://zhidao.baidu.com/question/433674777678342524.html
https://wenku.baidu.com/view/3821f41680c4bb4cf7ec4afe04a1b0717fd5b3e4.html
https://docs.microsoft.com/zh-cn/samples/browse/?redirectedfrom=MSDN-samples
https://blog.csdn.net/xianfajushi/article/details/7493697?reload
https://blog.csdn.net/weixin_30750685/article/details/111895879
https://www.cnblogs.com/owenzh/p/13329350.html
http://www.luofenming.com/show.aspx?id=ART2018103000001
https://blog.csdn.net/xin12345679/article/details/115124035

C# Coding Style
https://github.com/dotnet/corefx/blob/master/Documentation/coding-guidelines/coding-style.md