add keycodes note

docs/guide/keydown.md

@@ -5,7 +5,7 @@
 
 `selectOnKeyCodes {Array}` is an array of keyCodes that will trigger a typeAheadSelect. Any keyCodes
  in this array will prevent the default event action and trigger a typeahead select. By default, 
- it's just `[13]` for return. For example, maybe you want to tag on a comma keystroke
+ it's just `[13]` for return. For example, maybe you want to tag on a comma keystroke:
 
 <TagOnComma /> 
 
@@ -29,6 +29,9 @@ By default, the prop is a no–op returning the same object `map` object it rece
 maps keyCodes to handlers: `{ <keyCode>: <callback> }`. Modifying this object can override default
 functionality, or add handlers for different keys that the component doesn't normally listen for.
 
+Note that any keyCodes you've added to `selectOnKeyCodes` will be passed to `map-keydown` as well,
+so `map-keydown` will always take precedence.
+
 **Default Handlers**
 
 ```js