Add link with some 5a-75b hacking

[eibach]

In https://zeromips.org/posts/2022-05-29-5a-75b I have documented my modification of the 5a-75b board. I suppose this could be helpful/encouraging for others. As this github repo is the de facto standard documentation, maybe you could add a link to my post here.

[q3k]

I'll gladly add a link, but would you kindly file a PR? :)

[eibach]

Thanks, done.

[q3k]

Thank you!