docs/devel: make a statement about includes

While not explicitly disallowing header macro abuse (because that
would make us hypocrites) lets at least address some things to think
about.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Message-Id: <20230424092249.58552-17-alex.bennee@linaro.org>
1 file changed