fix(quay-docs):Remove commented-out 3.0-master downstream section from README.adoc - #1783

Vale found 3 issue(s). See annotations in the Checks tab.

Level 2, 3, 4, and 5 sections (=== and deeper) are not supported in DITA.

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/github-script@v7, tj-actions/changed-files@v40. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Assign [role="_abstract"] to a paragraph to use it as <shortdesc> in DITA.