 Could not find a version that satisfies the requirement schemagpt (from versions: none)

I want to use this project to convert NL to RDF-format. When I execute the command pip install schemagpt, I get this error: 

```Defaulting to user installation because normal site-packages is not writeable
ERROR: Could not find a version that satisfies the requirement schemagpt (from versions: none)
ERROR: No matching distribution found for schemagpt```

Anyone who can help? Thanks!

