[FR] Update documentation to reflect behavior of data_path variable

[pgarco]

Describe the solution you'd like

The variable data_path creates a new folder (in your example, "data/" creates a new folder in root with name data).

But the documentation does not specify that it creates a new folder, but rather that the .json files are saved in the path that is specified.

https://github.com/cjbarrie/academictwitteR/blob/master/README.md?plain=1#L202

I suggest clarifying:

## Data storage

Files are stores as JSON files in specified directory when a `data_path` is specified. Tweet-level data is stored in files beginning "data_"; user-level data is stored in files beginning "users_".

to

## Data storage

When a `data_path` is specified, a new directory is created, and the files are stored as JSON files inside the new directory. Tweet-level data is stored in files beginning "data_"; user-level data is stored in files beginning "users_".

Anything else?

No response