Added notice about supported backends

Signed-off-by: Dmitry Chepurovskiy <dm3ch@dm3ch.net>

cmd/helm/list.go

@@ -126,7 +126,7 @@ func newListCmd(cfg *action.Configuration, out io.Writer) *cobra.Command {
 	f.IntVarP(&client.Limit, "max", "m", 256, "maximum number of releases to fetch")
 	f.IntVar(&client.Offset, "offset", 0, "next release name in the list, used to offset from start value")
 	f.StringVarP(&client.Filter, "filter", "f", "", "a regular expression (Perl compatible). Any releases that match the expression will be included in the results")
-	f.StringVarP(&client.Selector, "selector", "l", "", "Selector (label query) to filter on, supports '=', '==', and '!='.(e.g. -l key1=value1,key2=value2)")
+	f.StringVarP(&client.Selector, "selector", "l", "", "Selector (label query) to filter on, supports '=', '==', and '!='.(e.g. -l key1=value1,key2=value2). Works only for secret(default) and configmap storage backends.")
 	bindOutputFlag(cmd, &outfmt)
 
 	return cmd