Update README.md

Author: jbaudanza

README.md

@@ -42,6 +42,8 @@ messages['ordinal-example']({ N: 1 });
 
 * [`locale`](https://messageformat.github.io/messageformat.js/doc/MessageFormat.html#MessageFormat) The [CLDR language code](http://www.unicode.org/cldr/charts/29/supplemental/language_territory_information.html) to pass to [messageformat.js](https://messageformat.github.io/messageformat.js/doc/MessageFormat.html). Defaults to `en`.
 * [`disablePluralKeyChecks`](https://messageformat.github.io/messageformat.js/doc/MessageFormat.html#disablePluralKeyChecks) By default, messageformat.js throws an error when a statement uses a non-numerical key that will never be matched as a pluralization category for the current locale. Use this argument to disable the validation and allow unused plural keys. Defaults to `false`.
+* [`intlSupport`](https://messageformat.github.io/messageformat.js/doc/MessageFormat.html#setIntlSupport) Enable or disable support for the default formatters, which require the Intl object. Defaults to `false`.
+
 
 ## License