Drafted a basic doc for tkn-plugins to resolve issue #1273

[Senjuti256]

Changes

Added a basic documentation for tkn plugins with reference to the issue #1273

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
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• Includes tests (if functionality changed/added)
• Run the code checkers with make check
• Regenerate the manpages, docs and go formatting with make generated
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Release Notes

NONE

[tekton-robot]

Hi @Senjuti256. Thanks for your PR.

I'm waiting for a tektoncd member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[piyush-garg]

/ok-to-test
/lgtm

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vinamra28

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