docs: refine multi-doc README note and machine.common helper comment

- README: clarify that not all multi-doc types are always present —
  HostnameConfig/ResolverConfig and one network interface document are
  always emitted, Layer2VIPConfig depends on floatingIP on controlplane,
  and RegistryMirrorConfig is cozystack-only.
- charts/cozystack _helpers.tpl: the talos.config.machine.common helper
  also renders nodeLabels for controlplane nodes — update the comment.

Assisted-By: Claude <noreply@anthropic.com>
Signed-off-by: Aleksei Sviridkin <f@lex.la>

Author: lexfrei

README.md

@@ -118,7 +118,7 @@ cluster:
 
 > **Note:** The output format depends on the Talos version configured in `Chart.yaml` (`templateOptions.talosVersion`) or via the `--talos-version` CLI flag.
 > For Talos < v1.12, the output is a single YAML document with `machine.network` and `machine.registries` sections (as shown above).
-> For Talos >= v1.12, the output uses the multi-document format with separate typed documents (`HostnameConfig`, `ResolverConfig`, `LinkConfig`, `BondConfig`, `VLANConfig`, `RegistryMirrorConfig`, `Layer2VIPConfig`) instead of the deprecated monolithic fields.
+> For Talos >= v1.12, the output uses the multi-document format with separate typed documents instead of the deprecated monolithic fields. `HostnameConfig`, `ResolverConfig` and a network interface document (`LinkConfig`, `BondConfig`, or `VLANConfig` — depending on topology) are always emitted; `Layer2VIPConfig` appears on controlplane nodes when `floatingIP` is set; `RegistryMirrorConfig` is emitted only by the cozystack chart.
 
 Apply config:
 ```bash

charts/cozystack/templates/_helpers.tpl

@@ -6,7 +6,7 @@
 {{- end }}
 {{- end }}
 
-{{- /* Shared machine section: type, kubelet, sysctls, kernel, certSANs, files, install */ -}}
+{{- /* Shared machine section: type, nodeLabels (controlplane), kubelet, sysctls, kernel, certSANs, files, install */ -}}
 {{- define "talos.config.machine.common" }}
 machine:
   {{- if eq .MachineType "controlplane" }}