Postdoc ad

[katyhuff]

Summary of changes

Adds an opening for a postdoc to the openings page.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] I have read the CONTRIBUTING document.
• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

Checklist for Reviewers

Reviewers should use this link to get to the Review Checklist before they begin their review.

[katyhuff]

Merging my own PR. It builds locally. I'd like to get this out quickly.