Add CI tutorials

[wangliang1989]

什么是CI？

[core-man]

什么是CI？

Continuous Integration (持续集成): https://docs.github.com/cn/actions/guides/about-continuous-integration

现在使用比较多的 CI 有 GitHub Actions，其他有 Travis CI。GMT, GMT-China, seismo-learn, SAC_zh 都使用 GitHub Actions 进行持续集成（代码位于 .github/ 目录），GitHub Actions 模板比较多，想要的CI基本都可以找到模板抄一下就可以了。

• GMT 早期使用 Travis CI，seisman 在 https://github.com/gmt-china/GMT_docs/pull/264 中更新为 GitHub Actions，可以通过仓库的 Actions(https://github.com/gmt-china/GMT_docs/actions) 查看 CI 运行状态
• SAC 中文手册在 https://github.com/seisman/SAC_Docs_zh/pull/165 后也由 Travis CI 迁移为 GitHub Actions

GitHub Actions Tutorials:

• Quick Start
• GitHub Actions 入门教程

[seisman]

Why do we need these tutorials.

[core-man]

Why do we need these tutorials.

Not a detailed tutorial but some links like those above in case some contributors want to know more about ci.

[seisman]

OK. it sounds good.