[Templating] Added a sentence that explains what a Template Helper is

Author: Iltar van der Berg

components/templating/introduction.rst

@@ -135,7 +135,8 @@ escaper using the
 Helpers
 -------
 
-The Templating component can be easily extended via helpers. The component has
+The Templating component can be easily extended via helpers. Helpers are PHP objects that 
+provide features useful in a template context. The component has
 2 built-in helpers:
 
 * :doc:`/components/templating/helpers/assetshelper`