README: remove Homebrew-specific things.
README: remove Homebrew-specific things.

Make this README more Linuxbrew focused.

maxim-belkin/brew,Linuxbrew/brew,hanxue/linuxbrew,Linuxbrew/brew,hanxue/linuxbrew,Linuxbrew/brew,hanxue/linuxbrew,maxim-belkin/brew,Linuxbrew/brew,maxim-belkin/brew