Recommended remove platformengineering.org vendor backed reference.

## Enhancement

The website platformengineering.org is heavily controlled by Humanitec, I would rather point to the Platforms WG inside of the CNCF or the WG whitepaper to avoid vendor references.

Inspect the repository's default files to locate the platformengineering.org reference; no specific file is named in the issue. Confirm whether the preferred replacement is the CNCF Platforms WG or its whitepaper, then update the reference and verify that no vendor-backed link remains.

Written by the indexing model from the issue text.