Add a worked out example of naming compound Elements'

[narration-sd]

Most people who use Craft/Yii's query builders are going to end up on Entry's doorstep -- perhaps beginning with Entry::find();

It would be very good to have a worked out example of how this works when wanting to sort, for currrent Slack question example, using orderBy() on a column. You can't use an alias for the table involved, so the tablename itself must be used, which I couldn't rapidly lay on hands for an example that this is correct, last night. But it is, except many won't have my foggy long memory of possibilities on such things.

This would be a great place also to explain just what the Entry structure is, so that the joins behind it are understood in principle, if not necessarily in detail -- hence the table names that would be used for various columns.