message: update setup guide
diff: ## About:
  -SymphonyElectron is a desktop client of the Symphony Communication Platform built for macOS, Windows 10 and Windows 7. We've built this using the popular [electron](https://github.com/electron/electron) framework to support cross platform desktop apps loaded in a chromium container
  +SymphonyElectron is a desktop client of the Symphony Communication Platform built for macOS, Windows 10, Windows 7
  + and Linux (experimental)
  +. We've built this using the popular [electron](https://github.com/electron/electron) framework to support cross platform desktop apps loaded in a chromium container.
  ## Contributing
  