To add a comment or remark in your Ubuntu crontab is trivially easy, following the standard for adding comments already found in bash scripting.

In other words, all you have to do in order to add a line which you don’t want the cron system to process, is start it off with the hash (#) character!

In practice:

# This is a comment and will not be processed by the cron engine
00 01 * * * ls -lh /home/craig

Nifty.