Merge branch 'master' into script-fixes

script/add-grammar

@@ -147,6 +147,10 @@ unless $url
   exit 1;
 end
 
+# Exit early if docker isn't installed or running.
+log "Checking docker is installed and running"
+command('docker', 'ps')
+
 # Ensure the given URL is an HTTPS link
 parts    = parse_url $url
 https    = "https://#{parts[:host]}/#{parts[:user]}/#{parts[:repo]}"