Develop Import/Export Data section

This section focusses on the use of CSV only at the moment, this needs to cover other forms of data access and creation to make it useful for users picking up Python.

* https://github.com/Public-Health-Scotland/python-training/pull/4#discussion_r2298095099
* https://github.com/Public-Health-Scotland/python-training/pull/4#discussion_r2298097623