Create a wakatime plugin

It would be nice to have a Wakatime plugin for Scratch as well, a lot of developers use (including me). I actually have the will to do it, but I'm not aware of the plugin interface capabilities/docs. It would be nice to have something pointing to it in the _README.md_.

首先找到 Scratch 的插件接口及其现有文档，然后检查 README.md，确定链接到插件指南的合适位置。确认 Wakatime 插件将如何与编辑器集成，并将完成标准定义为一个可运行的插件以及 README 中的引用。

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