As I understand, you are looking for something that will take code and text files in an existing Git repository and somehow automagically create a .ipynb file from them. I am not aware of any project/tool out there that does exactly what you want. However,
the Jupyter Notebook format is pretty well-defined and in fact you can probably re-use the nbformat Python module to code something up for this. See
https://github.com/jupyter/nbformat/tree/master/nbformat/v4. I imagine you can re-use the functions like `new_code_cell` and `new_markdown_cell`.
If by chance you are actually looking for a way to generate a Jupyter Notebook
server from a Git repository, which is a different problem, that is something that repo2docker can do:
https://github.com/jupyter/repo2docker