doc: update for core/formula separation

Library/Homebrew/manpages/brew.1.md

share/doc/homebrew/Acceptable-Formulae.md

share/doc/homebrew/Brew-Test-Bot-For-Core-Contributors.md

share/doc/homebrew/FAQ.md

share/doc/homebrew/Formula-Cookbook.md

...ow-To-Open-a-Homebrew-Pull-Request-(and-get-it-merged).md

share/doc/homebrew/Interesting-Taps-&-Branches.md

share/doc/homebrew/Migrating-A-Formula-To-A-Tap.md

share/doc/homebrew/Rename-A-Formula.md

share/doc/homebrew/Troubleshooting.md

share/doc/homebrew/brew-tap.md

share/doc/homebrew/brew.1.html

share/man/man1/brew.1