title: How can I add custom angular material mat-error
body: <p>I have a list of items and now I am adding data from input box to that list.
  I would like to show mat-error for duplicate entry under that input box.    </p>
  
  <pre><code>&lt;mat-form-field&gt;
      &lt;input matInput (keyup)="validation()" [(ngModel)]="package"&gt;
      &lt;mat-error&gt;Duplicate Entry&lt;/mat-error&gt;
  &lt;/mat-form-field&gt;   
  </code></pre>
  
  <p>Suggest me a proper way to tackle such a problem.</p>