feat: add CITATION.cff file

[milinddethe15]

What this PR does / why we need it:
It adds the label "Cite this repository" at right sidebar:

see at: https://github.com/milinddethe15/kf-katib/tree/feat/add-CITATION.cff

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #2544

Checklist:

• Docs included if any changes are user facing

[milinddethe15]

The resultant BibTeX is:

@misc{George_A_Scalable_and_2020,
author = {George, Johnu and Gao, Ce and Liu, Richard and Liu, Hou Gang and Tang, Yuan and Pydipaty, Ramdoot and Saha, Amit Kumar},
title = {{A Scalable and Cloud-Native Hyperparameter Tuning System}},
url = {https://arxiv.org/abs/2006.02085},
year = {2020}
}

[gaocegege]

Thanks for your contribution! 🎉 👍

[Electronic-Waste]

@milinddethe15 Thanks for this. Just a typo:)

/ok-to-test

[Electronic-Waste]

@milinddethe15 Thanks for this!

/lgtm
/assign @kubeflow/wg-automl-leads @astefanutti @helenxie-bit @mahdikhashan

[andreyvelich]

Thank you for this @milinddethe15!
/lgtm
/approve

[google-oss-prow]

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[milinddethe15]

/retest