Update release README with clear steps for release notes

[xtreme-sameer-vohra]

Context

The release steps mention generating release notes and how this can be done. However, it would be valuable to have the expected actions more clearly documented

For example, run the release notes jobs on semantically versioned repo

Addtional context

This was missed in the v1.3 release with 3 first time release leads.

• We didn’t run it for all repos
  • Wasn’t run for eventing-rabbitmq, eventing-kafka
  • Docs folks manually collected this and the release blog got incorrect info link

Ideal state

• running the release note generation process and adding it to a release is automated like the github release generation is.