Updates prop documentation for scrollableTarget

Author: ankeetmaini

README.md

@@ -73,7 +73,7 @@ name | type | description
 **endMessage** | node |  this message is shown to the user when he has seen all the records which means he's at the bottom and `hasMore` is `false`
 **style** | object | any style which you want to override
 **height** | number | optional, give only if you want to have a fixed height scrolling content
-**scrollableTarget** | node | optional, reference to a (parent) DOM element that is already providing overflow scrollbars to the `InfiniteScroll` component.
+**scrollableTarget** | node or string | optional, reference to a (parent) DOM element that is already providing overflow scrollbars to the `InfiniteScroll` component. *You should provide the `id` of the DOM node preferably.*
 **hasChildren** | bool | `children` is by default assumed to be of type array and it's length is used to determine if loader needs to be shown or not, if your `children` is not an array, specify this prop to tell if your items are 0 or more.
 **pullDownToRefresh** | bool | to enable **Pull Down to Refresh** feature
 **pullDownToRefreshContent** | node | any JSX that you want to show the user, `default={<h3>Pull down to refresh</h3>}`