Thank you and a little suggestion on docs

[lqu]

Thank you for sharing your great work and fun ideas! I like your way of documentation, examples, especially the copyright/license notice. I wonder if you can add more to the docs, such as the following.

• preconditions
  • does the calendar have to be blank?
  • does it depend on a certain version of GitHub environment?
• side effects
  • does running this app clear the existing calendar?
• idempotence
  • what happens if it's run twice with different input?

I know I can get the answers from reading the source code, and all should do that before they run any scripts downloaded from the internet. But there is a difference between the current behavior and your design goals.

Cheers,
lqu