Update README.md : cherry-pick of PR #1696's commit with me signing.

[tlaurion]

Discussion about this here:
#1682

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This takes @fhvyhjriur's #1696 commit and sign it with my signature.
This supersedes #1696 and closes #1682.

[tlaurion]

This is documentation related and signed. Merging.
Thanks @fhvyhjriur, please consider reviewing how to sign commits for next time, yo ucan see the burden of doing this cleanly and steps involved.

[fhvyhjriur]

I took a look at how this signing is possible but it does not look like its possible to be implemented in my workstyle.
How i changed the file: I took a look at https://github.com/linuxboot/heads/blob/master/unmaintained_boards/README.md and pressed the pencil button. I typed in what i expected the text should look like and pressed some web-browser buttons to make a PR.
This was easy to do and i can implement this in my workstyle the same way i wrote this text as a comment here. I hope it is fine if i continue to do PR the same way i did the last one.