Add Citation to Github Repo

[Jennifer-Oxborough]

Citation

If you use this project, please cite:

LIF initiative. LIF (Learner Information Framework). 2026.
GitHub repository: https://github.com/LIF-initiative/lif-core

[Jennifer-Oxborough]

There is a known bug logged due to the way citations render: https://github.com/orgs/community/discussions/188779