Annotation command previewer

I put together a small page to let you preview [annotation commands](https://docs.github.com/en/actions/reference/workflow-commands-for-github-actions#setting-an-error-message). Which section should this go under?

Repo: https://github.com/xt0rted/annotation-previewer
View: https://xt0rted.github.io/annotation-previewer/