bug#35431: Mention "cp -l a b is exactly equivalent to ln a b"

[積丹尼 Dan Jacobson]

On (info "(coreutils) cp invocation") at

   ‘-l’
   ‘--link’
        Make hard links instead of copies of non-directories.

Mention

    "Exactly equivalent to ln."

or

     "cp -l a b is exactly equivalent to ln a b."

Or if not, mention why.