Now the link of "OpenShift Pipelines based on Tekton" is https://openshift.github.io/pipelines-docs/ which is valid. Verified on 4.5.0-0.nightly-2020-04-09-192237
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHBA-2020:2409