Outdated item pipeline example about Deferred

[elacuesta]

The Take screenshot of item example says "This example demonstrates how to return a Deferred from the process_item() method", but that is no longer the case (async/await syntax is currently used).
I think we should remove that sentence and add a reminder about enabling the asyncio reactor.

Also, I wonder if it'd be good to also restore the previous Deferred example and keep both of them, since not all projects might be able/willing to switch to the asyncio reactor.

[Gallaecio]

I believe that the example now uses coroutines, but not asyncio, so it should work with a regular Twisted reactor.

PS: I used to mix the two of them as well until @kmike and @wRAR illuminated me.

[elacuesta]

I've read this article a few times, which shows how to use async/await independently from asyncio, but I still get confused sometimes. Might be time to read it again!
In any case, there is no Deferred in play anymore, that needs to be addressed.

[incognitozen]

The docs need an example of a spider with asynio enabled and used.

[Gallaecio]

A simple spider does not require asyncio, and a complex spider would not make for a good example.

On the other hand, it may be useful to cover, for example, an example item pipeline that uses an asyncio-based SQL client to record items in a database.