Every so often a bad idea is too well-formed to ignore. This is one of those.
github-banner encodes a scrolling pixel message into your GitHub contribution graph by writing dated commits, one per square, until the little green grid spells out whatever you told it to. It has tests. It has documentation. It handles the empty-repository case gracefully. It is, by any reasonable measure of craftsmanship, finished.
It is also a terrible idea, and the README says so four times before it says anything else. We built it because the question "could you?" would not go away, answered it, and are now leaving it on the shelf as a warning to ourselves and others. Your contribution graph is not a canvas. Please do not do this.
If you are going to ignore that, the source is on GitHub. We did warn you.