Add "How do I list all items?" to FAQ

[Minoru]

Can't come up with a satisfying wording right now, should probably grep the logs for real-world example. The most common repeating question I see on IRC is the one about getting items listed all in one window, not per-feed. The response is query feeds, of course. Now that we have a document called "FAQ" we should put some real FAQs in there.

[Minoru]

Oh look, we've had an FAQ list since before it was cool: https://code.google.com/archive/p/newsbeuter/wikis/UsefulTipsAndTricks.wiki