Demo with Angular FormGroup

[Halanson]

We like to use Slate-Angular in the context of angulars FormGroup. For example to validate a required input field. Something like:

<mat-form-field>
    <slate-editable 
        formControlName="requiredInput"
        required
        [editor]="editor"
        [keydown]="keydown()"
        [renderElement]="renderElement()"
        [renderText]="renderText()"
      >
    <mat-error ngIf="myForm.controls.requiredInput.errors['required']">
        This input is required.
    </mat-error>
</mat-form-field>

Could you add a demo on how to achieve this? Or point me in the right direction and I will provide a PR with a demo.