docs: experiment with readme

[kamilsk]

Motivation: avoid copy-pasting.

Details https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-readmes.

Context:

• https://github.com/octomation/go-module/blob/main/README.md
• https://github.com/octomation/go-module/blob/main/docs/pages/index.mdx

They are the same.