Deeplink with Branch.io Docs + Deprecate Firebase (#329)

* add branch io docs

* add branch io video link

* Formatting

* Fix links

* Apply suggestions from code review

Co-authored-by: pinkeshmars <[email protected]>

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Co-authored-by: Pinkesh <[email protected]>
Co-authored-by: pinkeshmars <[email protected]>

Author: PoojaB26