message: add link to operator plugin proposal to README
  related to
diff: @@ -28,3 +28,4 @@ The proposal process is defined in [proposals.md](./proposals.md).
  | Design pluggable support | `gfichtenholt` | Design specification of the pluggable architecture and support for multiple package formats | [Design in GDoc](https://docs.google.com/document/d/1z03msZRGsRvcRaom-yrvEwIWcEfNy6fSA5Zg28gjYvA/edit?ts=60bb08cb#) | Jun 1, 2021 | [#2944](https://github.com/kubeapps/kubeapps/issues/2944) |
  | Customizable UI for plugins | `@castelblanque` | Design proposal for the customization of UI only from backend, in order to ease the burden of maintaining UI hardcoded cases per plugin. | [Design in GDoc](https://docs.google.com/document/d/1wVYQmYO2TADYOKfabSdLhjnreBjExuB9VxRE8zvvR4o) | Jul 12, 2022 | [#4365](https://github.com/kubeapps/kubeapps/issues/4365) |
  | New multicluster design | [`@castelblanque`](https://github.com/castelblanque) | A new design for extending multicluster support to all package plugins. | [Design in GDoc](https://docs.google.com/document/d/1qYHIa5dd9qwxTdzyNUn7yXacwmYjH7R-KnnWxXkPItE/) | Oct 24, 2022 | [#5152](https://github.com/vmware-tanzu/kubeapps/issues/5152) |
  +| Operators Packaging Plugin | `gfichtenholt` | Initial thoughts on new Operators Packaging Plugin | [Design in GDoc](https://docs.google.com/document/d/18CUxhkaQAmIneUsTGOhtjNpokO-pr5dp/edit?usp=sharing&ouid=112444106102121063639&rtpof=true&sd=true) | Dec 20, 2022 | [#4920](https://github.com/vmware-tanzu/kubeapps/issues/4920) |
  