get_maintainer: add --no-foo options to --help

Many flag options are boolean and support both a positive and a negative
invocation from the command line.  Some of these are even mentioned by
example (e.g., --nogit is mentioned as a default option), but they aren't
explicitly mentioned in the list of options.  It happens that some of
these are pretty important, as they are default-on, and to turn them off,
you have to know about the --no-foo version.

Rather than clutter the whole help text with bracketed '--[no]foo', let's
just mention the general rule, a la 'man gcc'.

Signed-off-by: Brian Norris <[email protected]>
Signed-off-by: Joe Perches <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

scripts/get_maintainer.pl

@@ -845,6 +845,9 @@ sub usage {
       Entries in this file can be any command line argument.
       This file is prepended to any additional command line arguments.
       Multiple lines and # comments are allowed.
+  Most options have both positive and negative forms.
+      The negative forms for --<foo> are --no<foo> and --no-<foo>.
+
 EOT
 }