Shortcodes are content files specific.

This fixes spf13/hugo#440.

docs/content/extras/shortcodes.md

@@ -22,8 +22,10 @@ apply styling for display.
 
 To avoid both of these limitations Hugo created shortcodes.
 
-A shortcode is a simple snippet inside a markdown file that Hugo will render
+A shortcode is a simple snippet inside a content file that Hugo will render
-using a predefined template.
+using a predefined template. Note that shortcodes will not work in template 
+files - if you need a functionality like that in a template, you most likely
+want a [partial template](/templates/partial) instead.
 
 ## Using a shortcode