Documentation should explain what "closing" a job means

[gjcarneiro]

The documentation for Job.close() is very vague: https://aiojobs.readthedocs.io/en/stable/api.html#aiojobs.Job.close

coroutine close(*, timeout=None)
Close the job.

If timeout exceeded asyncio.TimeoutError raised.

The job is in closed state after finishing the method.

Yes, but what does "closing" a job really entail? I suspect cancellation via asyncio.Task.cancel(), but the only way of knowing is to read the source code.

(goes read the source)

Yes, indeed it does asyncio.Task.cancel(). That is good. But docs need to be more specific. Perhaps linking to the asyncio docs.

Suggestion of improved docstring:

Closes the job by means of requesting the underlying asyncio Task to be [cancelled](https://docs.python.org/3/library/asyncio-task.html#asyncio.Task.cancel).

[Dreamsorcerer]

Happy to review a PR with a change to the docs.

[Dreamsorcerer]

I think I've improved this in #495.