Add documentation for adding a TSC Member to the Release Manager team

[cdils]

Per #107, release managers require specific permissions to perform their role. This team should be documented, along with instructions to add/remove a release manager.

Suggest adding a release-manager.md file to the tsc/process folder.

[gopal10]

Please assign to me, I am working on this

[cdils]

Hi @gopal10 is there anything I can help with?

[cdils]

Just seeing #180 as a PR for this. Thank you @gopal10 and will review!