Move and redo Benefits section of README

[meg-gutshall]

thought: I think we should move this to become the first section of the Table of Contents, retitle it, and reword it a bit. When we original wrote it, we were trying to convince people why this would be a good idea. Now, people will already be at the repo when they see it so I think we should change it to present tense and clean it up a little. We can do this now or open a new issue to do it in a separate PR.

Originally posted by @meg-gutshall in #2 (comment)