Update README.md and manpage

[miccal]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

I can no longer commit my time to be a regular maintainer of brew.

I would like to continue as a member of brew, however, if that is possible.

Thank you.

[p-linnane]

Thank you for everything you have done for Homebrew @miccal. I will go ahead and remove your commit bit, but of course leave you as a member. I'll close this PR as there is a workflow that will handle those changes.

On a personal note: thank you so much for all your help when I started contributing. It was an honor to work alongside you 😄

[p-linnane]

@carlocab helpfully pointed out that that workflow doesn't add the 'former maintainers with significant contributions` section, so let's merge this.

[miccal]

Thank you @p-linnane and @carlocab.