Update install dependency-update help text

Signed-off-by: David Mládek <david.mladek.cz@gmail.com>

cmd/helm/install.go

@@ -145,7 +145,7 @@ func addInstallFlags(cmd *cobra.Command, f *pflag.FlagSet, client *action.Instal
 	f.StringVar(&client.NameTemplate, "name-template", "", "specify template used to name the release")
 	f.StringVar(&client.Description, "description", "", "add a custom description")
 	f.BoolVar(&client.Devel, "devel", false, "use development versions, too. Equivalent to version '>0.0.0-0'. If --version is set, this is ignored")
-	f.BoolVar(&client.DependencyUpdate, "dependency-update", false, "run helm dependency update before installing the chart")
+	f.BoolVar(&client.DependencyUpdate, "dependency-update", false, "update dependencies if they are missing before installing the chart")
 	f.BoolVar(&client.DisableOpenAPIValidation, "disable-openapi-validation", false, "if set, the installation process will not validate rendered templates against the Kubernetes OpenAPI Schema")
 	f.BoolVar(&client.Atomic, "atomic", false, "if set, the installation process deletes the installation on failure. The --wait flag will be set automatically if --atomic is used")
 	f.BoolVar(&client.SkipCRDs, "skip-crds", false, "if set, no CRDs will be installed. By default, CRDs are installed if not already present")