update contributors

[n-kall]

Summary

Adding my name to the contributors list (forgot to do this in any of the previous PRs).

Copyright and Licensing

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[paul-buerkner]

Right, thanks! I overlooked that too.