message: docs: Add asterisk info in template syntax guide
  Add helpful alert for asterisk syntax in the `ngFor` section of template syntax guide
  PR Close
diff: @@ -1600,6 +1600,14 @@ The following example shows `NgFor` applied to a simple `<div>`. (Don't forget t
  <code-example path="built-in-directives/src/app/app.component.html" region="NgFor-1" header="src/app/app.component.html"></code-example>
  +<div class="alert is-helpful">
  +
  +Don't forget the asterisk (`*`) in front of `ngFor`. For more information
  +on the asterisk, see the [asterisk (*) prefix](guide/structural-directives#the-asterisk--prefix) section of
  +[Structural Directives](guide/structural-directives).
  +
  +</div>
  +
  You can also apply an `NgFor` to a component element, as in the following example.
  <code-example path="built-in-directives/src/app/app.component.html" region="NgFor-2" header="src/app/app.component.html"></code-example>
  