Small updates to process doc

[cholmes]

Proposed Changes:

1. Update doc to remove openapi references and clearer instructions to update schema.

PR Checklist:

• This PR is made against the dev branch (all proposed changes except releases should be against dev, not master).
• This PR has no breaking changes.
• I have added my changes to the CHANGELOG or a CHANGELOG entry is not required.
• [ n/a ] This PR affects the STAC API spec, and I have opened issue/PR #XXX to track the change.

[m-mohr]

Made a minor change.

Edit: Oh, we conflicted...