declare index in ngfor code example

Example 1: ngfor index

<ul>
    <li *ngFor="let item of items; let i = index" [attr.data-index]="i">
        {{item}}
    </li>
</ul>

Example 2: ngfor get index

<ul>
    <li *ngFor="let item of items; let i = index" [attr.data-index]="i">
        {{item}}
    </li>
</ul>