[Doc] Fix typos and link errors for pipelines.md

[gavinfish]

Changes

Fix some typos and link errors for pipelines.md file

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[tekton-robot]

Hi @gavinfish. 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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[gavinfish]

@googlebot I signed it!

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[gavinfish]

/assign @dlorenc

[ghost]

/ok-to-test
/lgtm

[vdemeester]

/lgtm

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gavinfish, vdemeester

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