Improved documentation for <TextInput caretHidden=...>

Summary:
Documentation only.

Created from Diffusion's 'Open in Editor' feature.

Reviewed By: sahrens

Differential Revision: D6878890

fbshipit-source-id: 23f58246625ab6664bc3dcd4490f24ee50e410c8

Libraries/Components/TextInput/TextInput.js

@@ -591,6 +591,7 @@ const TextInput = createReactClass({
     ]),
     /**
      * If `true`, caret is hidden. The default value is `false`.
+     * This property is supported only for single-line TextInput component on iOS.
      */
     caretHidden: PropTypes.bool,
   },