Documentation/process: use scripts/get_maintainer.pl on patches

Explain that, when collecting list of people to Cc the patch,
scripts/get_maintainer.pl should be used on patches, not on the
directories.  The behavior is quite different, because with "-f" on
a directory, the maintainers of individual files will not be shown.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220427185645.677039-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>