docs(ngController): global controller fns disabled by default

Update doc to reflect 3f2232b,
which disabled use of global controller constructors (by default).

Closes #8466

Author: drewbarbs

src/ng/directive/ngController.js

@@ -23,10 +23,16 @@
  *
  * @element ANY
  * @scope
- * @param {expression} ngController Name of a globally accessible constructor function or an
- *     {@link guide/expression expression} that on the current scope evaluates to a
- *     constructor function. The controller instance can be published into a scope property
- *     by specifying `as propertyName`.
+ * @param {expression} ngController Name of a constructor function registered with the current
+ * {@link ng.$controllerProvider $controllerProvider} or an {@link guide/expression expression}
+ * that on the current scope evaluates to a constructor function.
+ *
+ * The controller instance can be published into a scope property by specifying
+ * `ng-controller="as propertyName"`.
+ *
+ * If the current `$controllerProvider` is configured to use globals (via
+ * {@link ng.$controllerProvider#allowGlobals `$controllerProvider.allowGlobals()` }), this may
+ * also be the name of a globally accessible constructor function (not recommended).
  *
  * @example
  * Here is a simple form for editing user contact information. Adding, removing, clearing, and