Adding documentation for PR #6819 (#1623)

Adding documentation for this feature: helm/helm#6819
not being aware of this, make turn helm2 to 3 migrations very complicated.

README.md

@@ -197,6 +197,14 @@ releases:
     # See https://github.com/roboll/helmfile/issues/642
     # (default "", which means the standard kubeconfig, either ~/kubeconfig or the file pointed by $KUBECONFIG environment variable)
     kubeContext: kube-context
+    # passes --disable-validation to helm 3 diff plugin, this requires diff plugin >= 3.1.2
+    # It may be helpful to deploy charts with helm api v1 CRDS
+    # https://github.com/roboll/helmfile/pull/1373
+    disableValidation: false
+    # passes --disable-openapi-validation to helm 3 diff plugin, this requires diff plugin >= 3.1.2
+    # It may be helpful to deploy charts with helm api v1 CRDS
+    # https://github.com/roboll/helmfile/pull/1373
+    disableOpenApiValidation: false
     # limit the maximum number of revisions saved per release. Use 0 for no limit (default 10)
     historyMax: 10
     # When set to `true`, skips running `helm dep up` and `helm dep build` on this release's chart.