Improve readme wording

Author: dabbott

README.md

@@ -96,7 +96,7 @@ The sandbox accepts the following props/parameters.
 
 | Title | Description | Default |
 | ------------------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------- |
-| **`preset`** | This sets reasonable defaults for other parameters. Options are `javascript`, `react`, and `react-native`. Experimental options are `html` and `python` - make sure to lock down your javascript-playgrounds library version if you use these, since they may change. | `'javascript'` |
+| **`preset`** | This sets reasonable defaults for other parameters. Options are `javascript`, `react`, and `react-native`. Experimental options are `html` and `python` (make sure to lock down your javascript-playgrounds library version when using experimental presets).  | `'javascript'` |
 | **`title`** | An optional title for the editor pane. | `''` |
 | **`code`** | The code to show/run in the player. | The sample app |
 | **`files`** | A map of `{ [filename]: code }`. This will take precedence over `code` if given. | `undefined` |