UX: cover common use case of building plan offline. FIX: --diff-mode parameters

Author: needleshaped

docs/cli.md

@@ -40,6 +40,8 @@ This command renders `helmwave.yml.tpl` to `helmwave.yml`.
 
 Helmwave builds plan in complete plan directory (`.helmwave` by default) that other commands use.
 
+Build process by default includes check against manifests of specific :simple-kubernetes: Kubernetes version (taken online), as well as diff. To build plan offline, combine `--diff-mode=local` or `--diff-mode=none` with [`offline_kube_version`](yaml/#offline_kube_version).
+
 A plan includes:
 
 - Downloaded remote charts

docs/flags/diff-mode.md

@@ -3,8 +3,10 @@
 > Introduced in [:material-tag: v0.12.0](https://github.com/helmwave/helmwave/releases/tag/v0.12.0)
  
 
-- `live` - diff with live cluster
-- `plan` - diff with local plan
+- `live` - diff with live :simple-kubernetes: cluster
+- `local` - diff with local plan
 - `none` - disable diff
 
+Combine `--diff-mode=local` or `--diff-mode=none` with `offline_kube_version` to build a plan without kubernetes.
+
 ![diff example](assets/diff.png)