Fix 'Edit this page' and 'Create an issue' links on the website

Add a cascading page property to the frontmatter of docs/README.md
that will apply to all child pages displayed in the CLI section
of the docs on the website.

This ensures that the 'Edit this page' and 'Create an issue' links
in the the sidebar point to the CLI repo instead of the website repo.

docs/README.md

@@ -4,6 +4,8 @@ linkTitle: "CLI"
 weight: 5
 description: >
   Command-Line Interface
+cascade:
+  github_project_repo: https://github.com/tektoncd/cli
 ---
 
 {{% pageinfo %}}