update docs

README.md

@@ -20,6 +20,8 @@ If you're interested in developing on Bubble, see the [**Bubble Developer Guide*
 Once your Bubble is running, any device can connect to it: Windows, Linux, Mac, iOS, Android;
 if it supports VPN connections, it will probably work just fine.
 
+The Bubble itself runs Ubuntu 20.04 and can be launched in a variety of ways.
+
 To launch your own Bubble using this software, you will need either:
  * A system with Docker installed, to run the [Bubble Docker Launcher](docs/docker-launcher.md)
  * A Mac or Linux system, to run the launcher and/or build from source