bug#49193: Document require-final-newline vs. readonly files

[積丹尼 Dan Jacobson]

>>>>> "EZ" == Eli Zaretskii <eliz@gnu.org> writes:
>> From: 積丹尼 Dan Jacobson
>> <jidanni@jidanni.org>
>> Date: Wed, 23 Jun 2021 23:14:56 +0800
>> 
>> (info "(emacs) Customize Save") says:
>> If the value of the variable ‘require-final-newline’ is ‘t’, saving or
>> writing a file silently puts a newline at the end if there isn’t already
>> one there.  If the value is ‘visit’, Emacs adds a newline at the end of
>> any file that doesn’t have one, just after it visits the file...
>> 
>> OK, but mention if this even affects readonly files / owned by other users
>> that we visit.

EZ> There's nothing to mention, because this feature doesn't change how
EZ> saving to an unwritable file behaves in Emacs.  The feature works on
EZ> the buffer text, not on the buffer's file.

Ah, that clears things up.
So please mention that.