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.