Finalize the "Modeling Data Workflows" page

[bbockelm]

I believe the work in the "modeling data workflows" activity are all wrapped up (https://iris-hep.org/projects/modeling.html). Let's scrub the page to make sure everything is correct and we list it as wrapping up at the end of the design phase.

[ddavila0]

@fkw888 is there anything you want me to add in here?