README: Update Brewfile example
README: Update Brewfile example

- Alphabetize the list of things, and put `tap` lines at the top.
- Don't include formulae options, as they have been deprecated for some
  time and won't work.
- Use homebrew/cask-fonts instead of caskroom/fonts.
- Homebrew also works with taps hosted on non-standard (ie not GitHub)
  repo hosts, so use a fake example for illustration rather than
  Homebrew itself.
- Add blank lines for readability.

Homebrew/homebrew-bundle