add message when just outputting schedule file

lib/whenever/command_line.rb

@@ -39,6 +39,8 @@ module Whenever
         write_crontab(whenever_cron)
       else
         puts Whenever.cron(@options)
+        puts "[message] Above your schedule file converted to cron syntax; your crontab file was not updated."
+        puts "[message] Run `whenever --help' for more options."
         exit(0)
       end
     end