Description of problem:

This task captures the effort spent to address the missing documentation for tekton chains. Upstream issue - https://github.com/tektoncd/chains/issues/1275

Acceptance criteria: 

A new user is able to follow the tutorial and successfully configure the storage backend as GCS for chains.

Definition of Done:

Upstream tutorial reviewed and merged.

Build Details:

Additional info (Such as Logs, Screenshots, etc):

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