Success control on Winbond W25Q64JV flash

[IlysvlVEizbr]

It has been tested that the W25Q64JV can be successfully controlled using this repo.

According to the experiment, cmd5 arg must be False, otherwise:
if cross boundary:
　Readback is always 0
else:
　test pass

[peterhinch]

Thank you. I have updated README.md.