Improve error message

lib/site.rb

@@ -8,8 +8,8 @@ require 'rss'
 if ENV['KIOSKS_SITEURL']
   SITEURL = ENV['KIOSKS_SITEURL']
 else
-  puts "KIOSKS_SITEURL environment variable must be set to the base URL of the site without a trailing slash"
-  puts "eg https://kiosks.adrianshort.org"
+  puts "KIOSKS_SITEURL environment variable must be set to the base URL of the site without a trailing slash, eg:"
+  puts "export KIOSKS_SITEURL=https://kiosks.adrianshort.org"
   exit 1
 end