Update README. Related #59.

README.md

@@ -65,6 +65,8 @@ d3.selectAll(".orange").transition(t)
     .style("fill", "orange");
 ```
 
+If the specified *transition* is not found on a selected node or its ancestors (such as if the transition [already ended](#the-life-of-a-transition)), the default timing parameters are used; however, in a future release, this will likely be changed to throw an error. See [#59](https://github.com/d3/d3-transition/issues/59).
+
 <a name="selection_interrupt" href="#selection_interrupt">#</a> <i>selection</i>.<b>interrupt</b>([<i>name</i>]) [<>](https://github.com/d3/d3-transition/blob/master/src/selection/interrupt.js "Source")
 
 Interrupts the active transition of the specified *name* on the selected elements, and cancels any pending transitions with the specified *name*, if any. If a name is not specified, null is used.