docs: Document security implications of debugging

docs: Document security implications of debugging

Now that the GDB stub explicitly implements reading host files (note
that it was already possible by changing the emulated code to open and
read those files), concerns may arise that it undermines security.

Document the status quo, which is that the users are already
responsible for securing the GDB connection themselves.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230621203627.1808446-8-iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230630180423.558337-38-alex.bennee@linaro.org>