README.md: Add link to Homebrew blog
README.md: Add link to Homebrew blog

Inspired by https://github.com/Homebrew/brew/issues/8096 and https://github.com/Homebrew/brew/pull/8098. I think the blog is an important way for regular users to keep up-to-date with Homebrew evolution, so it deserves an entry in the main docs page.

Update docs/README.md

Co-authored-by: Mike McQuaid <a17fed27eaa842282862ff7c1b9c8395a26ac320@mikemcquaid.com>

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