Command helpText indicates that options must come before template.

command/build/help.go

 package build
 
 const helpText = `
-Usage: packer build TEMPLATE
+Usage: packer build [options] TEMPLATE
 
   Will execute multiple builds in parallel as defined in the template.
   The various artifacts created by the template will be outputted.

command/validate/help.go

 package validate
 
 const helpString = `
-Usage: packer validate TEMPLATE
+Usage: packer validate [options] TEMPLATE
 
   Checks the template is valid by parsing the template and also
   checking the configuration with the various builders, provisioners, etc.

website/source/docs/extend/command.html.markdown

@@ -52,7 +52,7 @@ it is not required. You're allowed to make the help look like anything
 you please.
 
 ```
-Usage: packer COMMAND ARGS...
+Usage: packer COMMAND [options] ARGS...
 
   Brief one or two sentence about the function of the command.