Add split docs

website/source/docs/configuration/interpolation.html.md

@@ -72,6 +72,11 @@ The supported built-in functions are:
       only possible with splat variables from resources with a count
       greater than one. Example: `join(",", aws_instance.foo.*.id)`
 
+  * `split(delim, string)` - Splits the string previously created by `join` 
+      back into a list. This is useful for pushing lists through module 
+      outputs since they currently only support string values.
+      Example: `split(",", module.amod.server_ids)`
+
   * `lookup(map, key)` - Performs a dynamic lookup into a mapping
       variable.