add documentation to include, fixes #163

lib/liquid/tags/include.rb

@@ -1,4 +1,19 @@
 module Liquid
+
+  # Include allows templates to relate with other templates
+  #
+  # Simply include another template:
+  #
+  #   {% include 'product' %}
+  #
+  # Include a template with a local variable:
+  #
+  #   {% include 'product' with products[0] %}
+  #
+  # Include a template for a collection:
+  #
+  #   {% include 'product' for products %}
+  #
   class Include < Tag
     Syntax = /(#{QuotedFragment}+)(\s+(?:with|for)\s+(#{QuotedFragment}+))?/o