Fix link to "why arent pipelineresources in beta"

[bobcatfish]

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[tekton-robot]

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[tekton-robot]

This PR cannot be merged: expecting exactly one kind/ label

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[bobcatfish]

/kind documentation

[pritidesai]

/lgtm

the following link is broken as well 🤪

To ease migration away from `PipelineResources`
[some types have an equivalent `Task` in the Catalog](#pipelineresource-equivalent-catalog-tasks).

[tekton-robot]

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