add --output-dir to documentation

docs/helm/helm_template.md

@@ -31,6 +31,7 @@ helm template [flags] CHART
       --name-template string   specify template used to name the release
       --namespace string       namespace to install the release into
       --notes                  show the computed NOTES.txt file as well
+      --output-dir string      writes the executed templates to files in output-dir instead of stdout
       --set stringArray        set values on the command line (can specify multiple or separate values with commas: key1=val1,key2=val2)
   -f, --values valueFiles      specify values in a YAML file (can specify multiple) (default [])
 ```
@@ -49,4 +50,4 @@ helm template [flags] CHART
 ### SEE ALSO
 * [helm](helm.md)	 - The Helm package manager for Kubernetes.
 
-###### Auto generated by spf13/cobra on 7-Nov-2017
+###### Auto generated by spf13/cobra on 15-Nov-2017