Load Existing RTF file to MUIRichTextEditor  

## Checklist

- [x] This is not covered in the [repository examples](https://github.com/niuware/mui-rte/tree/master/examples).
- [x] I am using the package [latest version](https://github.com/niuware/mui-rte/releases/latest).
- [ ] This is a bug report or an enhancement proposal.

## Description

Is there a way to load data from existing RTF file or RTF content to MUIRichTextEditor? 
