docs/devel/testing/fuzzing: Note that you can get qtest to read from a file

docs/devel/testing/fuzzing: Note that you can get qtest to read from a file

It is possible to get qtest to read fuzzer reproducers from a file
rather than directly from stdio; this is useful when you want to run
QEMU under gdb to debug the failure.  Document how to do this, which
was previously only written down in the commit message for
5b18a6bf44b9 ("chardev: Allow setting file chardev input file on the
command line").

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Message-id: 20251028165236.3327658-1-peter.maydell@linaro.org