This is 200 lines of bash using the file system as a database. The term document store implies a database which this is not. How is this different than just writing files to a directory?
The point is the project seems a bit low-effort. The most complicated thing in that bash script is argument processing.
What is the added value of that project? does it come up with something new or interesting? a query language for data? an efficient data storage? no, it just store json files in directories. Sure the file system is already a database, but that project doesn't add anything to the file system.
What are the use cases of this project?