website: update docs for self

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

@@ -26,6 +26,11 @@ can reference static keys in the map with the syntax
 get the value of the `us-east-1` key within the `amis` variable
 that is a mapping.
 
+**To reference attributes of your own resource**, the syntax is
+`self.ATTRIBUTE`. For example `${self.private_ip_address}` will
+interpolate that resource's private IP address. Note that this is
+only allowed/valid within provisioners.
+
 **To reference attributes of other resources**, the syntax is
 `TYPE.NAME.ATTRIBUTE`. For example, `${aws_instance.web.id}`
 will interpolate the ID attribute from the "aws\_instance"