Add example use of template tag

Author: Mark Gibbs

docs/template_tags.rst

@@ -3,8 +3,16 @@
 Template tags
 =============
 
-The ``plotly_dash`` library provides the ``plotly_app`` template tag. This tag inserts
-a ``Dash`` app within a page as a responsive ``iframe`` element.
+Importing the ``plotly_dash`` library provides the ``plotly_app`` template tag::
+
+  {%load plotly_dash%}
+
+  {%plotly_item name="SimpleExample"%}
+
+This tag inserts
+a ``DjangoDash`` app within a page as a responsive ``iframe`` element.
+
+The tag arguments are:
 
 :name = None: The name of the application, as passed to a ``DjangoDash`` constructor.
 :slug = None: The slug of the application instance.
@@ -13,7 +21,7 @@ a ``Dash`` app within a page as a responsive ``iframe`` element.
               this ratio to set its height.
 :use_frameborder = "0": HTML element property of the iframe containing the application.
 
-At least one of ``da``, ``slug`` and ``name`` must be provided. An object identified by ``slug`` will always be used, otherwise any
+At least one of ``da``, ``slug`` or ``name`` must be provided. An object identified by ``slug`` will always be used, otherwise any
 identified by ``name`` will be. If either of these arguments are provided, they must resolve to valid objects even if
 not used. If neither are provided, then the model instance in ``da`` will be used.