bug#39979: 28.0.50; `mouse-wheel-tilt-scroll' docstring is unclear/incomplete

[martin rudalics]

> A patch is attached which is proposed as a tentative improvement. If
> it’s good enough to apply, I do have my copyright assingment paperwork
> done so it can be committed right away.

Thanks for looking into this.  But

-  "Enable scroll using tilting mouse wheel."
+  "Enable horizontal scrolling via mouse or touchpad. Also see
+  ‘mouse-wheel-flip-direction’."

violates the rule from D.6 of the Elisp manual:

 The first line of the documentation string should consist of one or
     two complete sentences that stand on their own as a summary.

Also, 'mouse-wheel-flip-direction' does not have a great doc-string
either.  Maybe we should add a reference to section 21.1 of the Emacs
manual?

martin