Add root/sudo check

Add root/sudo check thanks to @bmullan

guac-install.sh

@@ -1,5 +1,8 @@
 #!/bin/bash
 
+# Check if user is root or sudo
+if ! [ $(id -u) = 0 ]; then echo "Please run this script as sudo or root"; exit 1 ; fi
+
 # Version number of Guacamole to install
 GUACVERSION="0.9.14"