Improve repos.csv documentation

[mike-solomon]

There is more nuance to what columns are or are not required than what's listed in our creating a repos csv doc.

We need to update that to provide additional context. As part of this, I feel like it would be beneficial to provide an example repos.csv file for each of the use cases in that file.

More information on feedback of what's wrong can be found in this Slack thread: https://moderneinc.slack.com/archives/C01S4M53THT/p1756406799864239

[mike-solomon]

Updated this page to include more accurate requirements for the variables -- still need to figure out better examples for the repos.csv stuff. dba4a60