Update CONTRIBUTING.md

[CatherineF-dev]

What this PR does / why we need it:

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)

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 #

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: CatherineF-dev
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[dgrisonnet]

/triage accepted
/assign

[k8s-triage-robot]

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This bot triages PRs according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
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/lifecycle stale

[CatherineF-dev]

/remove-lifecycle stale