doc: add documentation for To and When

[le0tan]

What type of PR is this?

docs

What this PR does / why we need it (en: English/zh: Chinese):

en: add documentation for To and When zh: 添加To和When的使用文档

Which issue(s) this PR fixes:

Fixes #5

[le0tan]

@ycydsxy the linter check failed: What went wrong here?

[Sychorius]

@ycydsxy the linter check failed: What went wrong here?

Looks weird, I'll try fixing it later🤔

[ycydsxy]

Rerun works