Release guide: is this still being used, does it need updating or should it be dropped?

From https://github.com/etcd-io/etcd/issues/12923#issuecomment-844310107:

> Thanks all for your feedback so far.
>
> I noticed that there's a **[Release guide](https://etcd.io/docs/next/dev-internal/release/)** - from `etcd.io/docs/next/dev-internal/release/`. A few questions about this guide:
>
> * Is [Release guide](https://etcd.io/docs/next/dev-internal/release/) actively being used?
> * Is it considered up-to-date?
> * If not, who can update it?
> * It probably makes more sense to add a template for release notes to the [Release guide](https://etcd.io/docs/next/dev-internal/release/), rather than as a separate `.md` file under etcd (as I had proposed in #13009). Thoughts?

/cc @hexfusion @ptabor @gyuho @spzala @nate-double-u