bug#64693: Documentation for the definition of a Menu Item

[uzibalqa via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Have been looking at the documentation for 'DEF' in 'define-key'.

(define-key KEYMAP KEY DEF &optional REMOVE)

DEF, the definition of a Menu Item is described in form as 

   (menu-item item-name binding . item-property-list)

Note that DEF constitutes a single list.  The special
dotted notation indicates that 'item-property-list' is not
a separate list but rather enables any number of property
elements in the form of ':keyword value' within the same
list structure.

But such detail is not properly described.  Pointing out how
the description of 'Cons Cells' and 'Dotted Notation' is sketchy
at best in the 'Elisp Reference Manual', and non-existent  in 
the 'Introduction to Programming in Emacs Lisp',  the aforementioned
description should be added in the documentation of 'define-key'.

Furthermore, a more comprehensive explanation of Cons Cells, Dotted
Notation, and Backquote Construct, should be introduced and backed up 
with real-life syntax such as the one described here.