Add schedule-x

[tomosterlund]

Checklist:

• I've read and understood Contributing Guidelines.
• I've added the new resource at the end of its section.
• This resource is out there for a while, and actively maintained.
• This resource is popular enough and has at least a few hundred stars on GitHub.

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Schedule-X is a project of rising popularity, which aims to complement the current market of calendars, with an event calendar that adheres to the Material Design 3 specification.

...

[tomosterlund]

Thanks for the review 👍

Just double-checking since the PR is open but approved: am I expected to do anything here?

[Ashe-reset]

这是来自QQ邮箱的假期自动回复邮件。   您好，我最近正在休假中，无法亲自回复您的邮件。我将在假期结束后，尽快给您回复。

[gokaygurcan]

All good. Thanks!