bug#31311: 27.0; doc of `pcase'

[Eli Zaretskii]

> From: Michael Heerdegen <michael_heerdegen@web.de>
> Cc: Drew Adams <drew.adams@oracle.com>,  31311@debbugs.gnu.org
> Date: Sun, 29 Apr 2018 20:31:59 +0200
> 
> > What you see in the manual is mostly the result of desperate efforts
> > of a single individual to have something remotely palatable in our
> > documentation.
> 
> My impression was more that there were diametral conceptions of how a
> good documentation would look like.

There's nothing special about this feature that should present
conceptual problems for documenting it well, any more than any other
advanced feature of which we have dozens in the ELisp manual.