Add documentation for release process

[ayberk]

Adds documentation for the release process. It's meant to be followed step by step, top-down.

Note that this is modified version of authenticator release process.

[k8s-ci-robot]

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[coveralls]

Pull Request Test Coverage Report for Build 1545

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 81.196%

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Totals
Change from base Build 1542:	0.0%
Covered Lines:	1697
Relevant Lines:	2090

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💛 - Coveralls

[wongma7]

must specify remote like

git push upstream v0.8.0

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ayberk

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[wongma7]

I think we should always do a "dry-run" -rc.0 or -alpha.0 pre-release. Would have helped in the most recent release , since there is no way to retry the Prow GCR build

[wongma7]

/lgtm