Add JOSS reference

[bhazelton]

Description

Add citation information for our JOSS paper to the readme.

Motivation and Context

Checklists:

Documentation Change Checklist:

• [x] I have read the contribution guide.
• [x] My code follows the code style of this project. Documentation change checklist:
• [ ] Any updated docstrings use the numpy docstring format.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (88932f3) to head (4c10c73). Report is 25 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #247 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 5 5 Lines 2131 2131 Branches 608 608 ========================================= Hits 2131 2131 ```

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