README.md: Mention CentOS and Red Hat
README.md: Mention CentOS and Red Hat

See Homebrew/linuxbrew#310

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