Provide examples of common scheduling operations

[Kingdutch]

While I understand that for end-user projects the recommended way to interact with the Revolt Event Loop is to use a package like Amphp or React, for maintainers of large frameworks (such as Drupal) there is significant overhead and impact to including new dependencies. These frameworks will still need to schedule some of their own tasks.

By providing examples of some common scheduling tasks such as concurrently or stream we can make it easier for framework maintainers to confidently adopt the Revolt Event Loop.