bug#66677: Missing documentation for multi-line Package-Requires

[Jonas Bernoulli]

Hello,

Since bug#36301 Package-Requires can be split across multiple lines, but
info node `(elisp) Library Headers' still claims that this has to be fit
on a single line.

This works now:

;; Package-Requires: ((emacs "25.1")
;;                    (compat "29.1.4.1"))

as does

;; Package-Requires: (
;;     (emacs "25.1")
;;     (compat "29.1.4.1"))

I.e., some non-whitespace has to be placed on the same line as
"Package-Requires:".

     Cheers,
     Jonas