Improve documentation for updating file sets using bulkrax / CSV

[ShanaLMoore]

Summary (request from Nick S.)

The documentation for updating file sets using Bulkrax is lacking, according to Annamarie. Let's make the documentation surrounding that functionality clear, so novice hyku / hyrax admins can use it.

Context here: https://samvera.slack.com/archives/C4TPN8ZT6/p1755619279928989

https://github.com/samvera/bulkrax/wiki/CSV-Importer

Task

Walk through how to do it with Annamarie - capture her areas of confusion.

Create documentation that would have made it easy for her to perform the updates

Acceptance Criteria

1. Documentation is created
2. Annamarie likes it, and thinks it meets the needs of users
3. Any potential marketing / blog / linkedin posts about how it works and the value of the functionality has been created and shared