Add service credential rotation feature doc

[jochenehret]

No description provided.

[stephanme]

Invited @beyhan for review since he is an author of the rfc-0040-service-binding-rotation.

[anita-flegg]

I would have made these changes myself, but I can no longer push changes without forking.
I'm not sure whether this was a deliberate change, but was was certainly easier when I had full permissions.

[beyhan]

I would have made these changes myself, but I can no longer push changes without forking. I'm not sure whether this was a deliberate change, but was was certainly easier when I had full permissions.

@anita-flegg We've activated branch protection rules by default, which means direct pushes to repositories aren't allowed anymore. When people even approver propose changes, they need to go through a pull request first. Since this particular PR is based on a fork, you won't be able to make direct changes to it. I'm not aware of any other permission changes. Please reach out to me via Slack if you have further question.