Add README for the data and formatter layers.

[RafsanNeloy]

Added a local README file for the top level folders data and formatter
Closes #28

[RafsanNeloy]

Do we want to hyperlink of this file or this is okay?

[RafsanNeloy]

Can you please give me suggestion how can I improve this more?

[dlq]

Could you put some more details and refine the focus of this in light of what is in plan.md?

[dlq]

Thanks for adding these READMEs. The overall structure is helpful, but two descriptions should be corrected before merging:

1. The data/ directory is not strictly for fetching raw objects. It also performs state-changing operations such as uploads, deletes, moves, tag updates, and project switching. Please describe it more broadly as the API interaction layer.
2. The example output for cbrain file list does not match the current implementation. The actual formatter displays ID, Type, and File Name, without size or status. Please replace it with real output or clearly label it as a conceptual example.

The checks are passing, and otherwise the documentation looks good!