So the public can "brew install" tailscale and start it as a global boot daemon via brew services.
supported: Homebrew 3.0, go1.15 darwin/amd64, macOS Catalina 10.15.3, Intel 64-bit
probably also but unconfirmed: BigSur 11 and Apple M1 ARM64
NOTE: lots of upgrades and polish since 1st squashed WIP PR, and applies most prior feedback
Part of #177. (WIP)
Signed-off-by: Mike Kramlich <groglogic@gmail.com>