You might have never been introduced to Sequence diagrams. A simple diagram can share your idea with the world. Playing software Indiana Jones and going through the code would give you the current state of the project, but code is easier to write than read. Also non-developers don't always read code. If the code is written in an obscure language having a diagram can be helpful. There are other ways to provide documentation but this one is fairly common.
This article is worth a read:
What tools and resources are available to build these?