Update README: Get cert before running setup script

[cvalarida]

I ran the automated script without setting up the cert first and got an error because it expected it. I got the cert, reran the script, and it all worked out.

Not sure who to ask for a review from, so I'll just @mention GitHub's suggested reviewers, @knkski, @robbiethegeek, and @markolson.

[ayaleloehr]

Also tagging @omgitsbillryan because it's ID.me related.

[jcmeloni-usds]

These what you're looking for? https://github.com/department-of-veterans-affairs/vets.gov-team/tree/master/Products/Identity/Files_From_IDme/development-certificates

[jcmeloni-usds]

Oh, this isn't "i have an issue" it's "instructions need to be updated". my bad. will read better in the future.

[omgitsbillryan]

So you

1. Moved the cert/key section up
2. Fixed link
3. Touched up some formatting

Big fat LGTM from me 👍

[markolson]

Maybe we could update bin/setup-osx to touch (or even try to grab) those files too?

[robbiethegeek-usds]

@cvalarida this looks great, I think if you can update the setup-osx and ping @markolson and it should be merged in.

[cvalarida]

Yeah, I thought about updating the script, but I'm not super confident in my bash-fu. I'll give it the ol' college try, though!

[cvalarida]

Turns out this became more of a fix-setup-script than a fix-readme kind of branch, but that's for the better. Bash-fu to the rescue!