Mention how Flux is used

[stefanprodan]

I've been looking at the repo docs and content and while I see the use of GitOps I think for clarity this repo should tell users that GitOps is implemented with FluxCD and the deployment orchestration with Flux HelmReleases and IaC controllers. Maybe a digram would also help.

Also tf-controller has been renamed and moved to this org: https://github.com/flux-iac/tofu-controller I think it would be good to switch the repo to the new controller.