Add a link from API Policy to Deprecations Table

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Changes

In a prior commit we added a table of deprecations which lists
the earliest date at which deprecated features can be removed
in line with our API policy.

This commit adds a link to the deprecations table from the API
policy document.

Suggested in previous PR comment.

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes docs (if user facing)
• Commit messages follow commit message best practices

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/test pull-tekton-pipeline-build-tests

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/test pull-tekton-pipeline-build-tests

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/test pull-tekton-pipeline-build-tests

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/test pull-tekton-pipeline-build-tests

[vdemeester]

/lgtm

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vdemeester

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[vdemeester]

/test pull-tekton-pipeline-build-tests

[bobcatfish]

Thanks @sbwsg !

/lgtm

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level=error msg="Running error: context loading failed: no go files to analyze"
level=error msg="Timeout exceeded: try increasing it by passing --timeout option"
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==== BUILD TESTS FAILED ====
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/test pull-tekton-pipeline-build-tests