Remove "Support for Linux coming soon" from README

[michael-staffa]

According to the blame, this statement was added to the README more than 6 years ago. Given that time frame my guess is we won't see Linux support for this anytime soon, so it would be a relatively small and more honest change.

Don't misunderstand, I don't care much one way or another; the manual steps are simple enough to follow on Linux. It's mainly because a few different video tutorials reference that statement.