Batch pull request description updated

Batch pull requests tend to find people at an awkward moment: a red check on a pull request they have never seen, or a notification about a branch nobody on the team pushed. A batch pull request now answers the obvious question first, with a note at the top saying Mergify opened it and nobody needs to act on it.

The note names the batch and the queue it was opened for and, when it matters, warns that pushing to the batch pull request or closing it takes your pull requests out of the queue. Underneath, the description walks through the rest:

• What it tests: your pull requests, applied in order on top of the base branch and everything queued ahead of them.
• Where it stands: the current state of the batch and the checks it is still waiting on.
• What happens next: what Mergify does when the checks pass or fail, based on your queue configuration.
• How it ends: how your pull requests get merged, depending on your merge method. The full merge conditions and the queue graph are still there, folded away below the explanation. There is nothing to turn on: every batch pull request the queue opens reads this way. So the next time someone asks what that batch pull request is doing, it can answer for itself.