Add doc links for 0.27.2 and 0.27.3

[ghost]

Changes

We released 0.27.3 today, so we need the doc links added to the README.md doc.

I forgot to make this equivalent PR for 0.27.2 so I'm adding links for both
.2 and .3 as part of this commit.

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Docs included if any changes are user facing
• Follows the commit message standard
• Meets the Tekton contributor standards (including
  functionality, content, code)
• Release notes block below has been filled in or deleted (only if no user facing changes)

Release Notes

NONE

/kind documentation

[pritidesai]

thanks @sbwsg

[vdemeester]

/lgtm
/retest

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[vdemeester]

Interesting…

1. integration tests are getting a bit flakey
2. we used to not run integration test on changes like this one (only README.md, docs/, …)

/retest