Add skeletal documentation of the emcraft-sf2 machine.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20210713142226.19155-3-peter.maydell@linaro.org
