servo: Update docs for layout mod

Source-Repo: https://github.com/servo/servo
Source-Revision: 731416b00c2f91e627daaaa0b407b866ea02aa1c

servo/src/servo/layout/layout.rs

@@ -1,6 +1,7 @@
 #[doc = "
 
-Builds display lists on request and passes them to the renderer
+The layout task. Performs layout on the dom, builds display lists and sends
+them to be rendered
 
 "];