Update templates.adoc

fixing the oc export all command.

Author: alberttwong

dev_guide/templates.adoc

@@ -646,7 +646,7 @@ template from there by adding parameters and other customizations. To export
 objects in a project in template form, run:
 
 ----
-$ oc export all --as-template=<template_name>
+$ oc export all --as-template=<template_name> > <template_filename>
 ----
 
 You can also substitute a particular resource type or multiple resources instead of `all`.