Update README.md (#750)

Author: 38elements

Diff for: docs/api/wrapper/README.md

@@ -8,7 +8,7 @@ A `Wrapper` is an object that contains a mounted component or vnode and methods
 
 ### `vm`
 
-`Component` (read-only): This is the `Vue` instance. You can access all the [instance methods and properties of a vm](https://vuejs.org/v2/api/#Instance-Properties) with `wrapper.vm`. This only exists on Vue component wrappers.
+`Component` (read-only): This is the `Vue` instance. You can access all the [instance methods and properties of a vm](https://vuejs.org/v2/api/#Instance-Properties) with `wrapper.vm`. This only exists on Vue component wrapper or HTMLElement binding Vue component wrapper.
 
 ### `element`