Merge pull request #31 from nstankov-bg/systemd

Added info and link to plutus-playground-systemd

book/docs/setup/Ubuntu.md

@@ -146,6 +146,12 @@ branch/commit. These probably won't happen often.
 Now we will run the Plutus Playground servers. We start these in a `nix-shell`
 which sets up the environment and has working versions of tools.
 
+**Note** Optionally, a project exists to control the two Plutus Playground
+servers as a systemd service, making start/stop/restart much less manual. See
+[plutus-playground-systemd](https://github.com/dino-/plutus-playground-systemd)
+for installation and configuration. If you use this, skip past the "terminal
+window" instructions below and access your new playground server in a browser.
+
 Open two terminal windows
 
 In terminal window 1