bug#31311: 27.0; doc of `pcase'

[Eli Zaretskii]

> From: Thien-Thi Nguyen <ttn@gnu.org>
> Date: Sun, 20 May 2018 20:59:58 +0200
> Cc: Michael Heerdegen <michael_heerdegen@web.de>
> 
> and the other remaining Issue (commit 455f990ce), excerpt here:
> 
>  +@c Issue: Should this be split off into its own node/subsection?
>  +@subheading Backquote-Style Patterns
>  +@cindex backquote-style patterns
> 
> IMHO, ‘pcase’ is so complex (compared to most other Emacs Lisp
> control structures), it deserves to be promoted to @‘section’,
> between ‘Conditionals’ and ‘Constructs for Combining Conditions’.
> 
> What do people think?

Why is this important?  You can always add subsections,
subsubsections, etc., if you want to structure the text into more
parts than it is already.