feat(docs): mention third parameter to `toSlateRange` method in the docs (#4416)
feat(docs): mention third parameter to `toSlateRange` method in the docs (#4416)

* Add third parameter to `toSlateRange` method

The `toSlateRange` method accepts an optional third parameter that is an object with property `exactMatch` and value is a boolean.

Example of this implementation can be found at the `Editable` component of `slate-react`, inside the custom `onDOMSelectionChange`.

* toSlateRange third param is optional

Co-authored-by: Dylan Schiemann <dd378c4ca75f71f527acddef5b43fc35b68d5b7a@dojotoolkit.org>

No changeset as it's a doc update.
ianstormtaylor/slate,ianstormtaylor/slate