document include tag parameters

site/docs/templates.md

@@ -192,6 +192,18 @@ Jekyll expects all include files to be placed in an `_includes` directory at the
 root of your source directory. This will embed the contents of
 `<source>/_includes/sig.md` into the calling file.
 
+You can also pass parameters to an include:
+
+{% highlight ruby %}
+{{ "{% include sig.textile param=value " }}%}
+{% endhighlight %}
+
+These parameters are available via Liquid in the include:
+
+{% highlight ruby %}
+{{ "{{ include.param " }}}}
+{% endhighlight %}
+
 ### Code snippet highlighting
 
 Jekyll has built in support for syntax highlighting of [over 100