readme: move informative stuff out of the list of actions in the release process

[maelvls]

I'm always tripping over this: It looks like another action, but isn't. It's an information instead. I propose to move the information to a note and reformulate this item as an action instead:

Before

2. A GitHub action will see the new tag and do the following:
   - Build and publish the container image at `quay.io/jetstack/venafi-agent`,
   - Build and publish the Helm chart at `oci://quay.io/jetstack/charts/venafi-kubernetes-agent`,
   - Create a draft GitHub release,
   - Upload the Helm chart tarball to the GitHub release.

After

2. Wait until the GitHub Actions finishes.

[wallrj]

/approve
/lgtm

[wallrj]

TIL about [!NOTE]. Thanks @maelvls 😄