Update README.md about the project being dead

[philcryer]

I finally got around to installing mist-ce in docker-compose, and it looked really promising... until I saw the news about Dell. Please update the README.md with info of the Dell buyout, and that they're not going to support or release mist-ce going forward. Also would be nice if you listed any active/promising forks going forward, I'm looking around but not seeing anything. It'd be a shame for all this work to just go away, again, I don't see a similar (open source) offering. Thanks for all the work, and here's hoping something positive comes of it.