Auto Format Option in README File!

Hi there,

Please also add the following option to the Readme file:

```
{"coc.preferences.formatOnSave": true}
```

[I found more information about it on Reddit!
](https://www.reddit.com/r/neovim/comments/12hlecb/cocprettier_config_file_warning_what_does_it_mean/)

I think it would be better to include it in the Readme file as well.