Update alevin-fry's references

[DongzeHE]

Dear scPCA team,

Thank you very much for brining scPCA to the community and choosing alevin-fry as the preprocessing tool!

I saw that the reference to alevin-fry might be outdated. It currently points to the preprint [He et al. 2021] (https://doi.org/10.1101/2021.06.29.450377) instead of our peer-reviewed paper He et al. 2023. It will be great if these references could be updated. Please let me know if you want me to submit a PR with the updated links!

Best, Dongze

[jaclyn-taroni]

Hi @DongzeHE, thanks for bringing this to our attention! We would welcome a pull request to update these references.

[DongzeHE]

Thanks, @jaclyn-taroni!