bug#19767: 25.0.50; cl-defgeneric docs

[Teodor Zlatanov]

I see lisp/emacs-lisp/cl-generic.el was added recently, and that's great.
But the CL manual hasn't been updated, I think?

The EIEIO manual for this functionality in (info "(eieio) Generics") and
(info "(eieio) Methods") is technically OK but for a *novice*, I think
it's almost incomprehensible and lacks examples.

I could try to help here, but I haven't used this facility before so I
need some pointers.

Thanks
Ted