scripts: kernel-doc: Translate the "Output format selection" subsection of OPTIONS

Another step in the direction of a uniform POD documentation, which will
make users happier.

Options land at the end of the script, not to clutter the file top.

The default output format is corrected to rst. That's what it is now.

A POD delimiting comment is added to the script head, which improves
the script logical structure.

Signed-off-by: Tomasz Warniełło <tomasz.warniello@gmail.com>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Disliked-by: Akira Yokosawa <akiyks@gmail.com>
Link: https://lore.kernel.org/r/20220218181628.1411551-5-tomasz.warniello@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

scripts/kernel-doc

@@ -52,6 +52,8 @@ See Documentation/doc-guide/kernel-doc.rst for the documentation comment syntax.
 
 =cut
 
+# more perldoc at the end of the file
+
 # 18/01/2001 - 	Cleanups
 # 		Functions prototyped as foo(void) same as foo()
 # 		Stop eval'ing where we don't need to.
@@ -81,11 +83,6 @@ sub usage {
     my $message = <<"EOF";
 Usage: $0 [OPTION ...] FILE ...
 
-Output format selection (mutually exclusive):
-  -man			Output troff manual page format. This is the default.
-  -rst			Output reStructuredText format.
-  -none			Do not output documentation, only warnings.
-
 Output format selection modifier (affects only ReST output):
 
   -sphinx-version	Use the ReST C domain dialect compatible with an
@@ -2563,3 +2560,27 @@ if ($Werror && $warnings) {
 } else {
     exit($output_mode eq "none" ? 0 : $errors)
 }
+
+__END__
+
+=head1 OPTIONS
+
+=head2 Output format selection (mutually exclusive):
+
+=over 8
+
+=item -man
+
+Output troff manual page format.
+
+=item -rst
+
+Output reStructuredText format. This is the default.
+
+=item -none
+
+Do not output documentation, only warnings.
+
+=back
+
+=cut