Add Release Signal YouTube playlist link to the handbook

[Vyom-Yadav]

What type of PR is this:

/kind documentation

What this PR does / why we need it:

• Adds the assignment Excel sheet to the VCS
• Adds Release Signal YouTube playlist link to the handbook

Which issue(s) this PR fixes:

None

Special notes for your reviewer:

/cc @Priyankasaggu11929 @pacoxu

[Priyankasaggu11929]

/lgtm /approve

/unhold

Feel free to remove hold whenever ready to merge.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Priyankasaggu11929, Vyom-Yadav

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files: - ~~[release-team/role-handbooks/release-signal/OWNERS](https://github.com/kubernetes/sig-release/blob/master/release-team/role-handbooks/release-signal/OWNERS)~~ [Priyankasaggu11929,Vyom-Yadav] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[Priyankasaggu11929]

/hold

I meant hold