docs(forms): add array example to get method (#41008)

PR Close #41008

packages/forms/src/model.ts

@@ -830,6 +830,17 @@ export abstract class AbstractControl {
    * -OR-
    *
    * * `this.form.get(['person', 'name']);`
+   *
+   * ### Retrieve a control in a FormArray
+   *
+   * When accessing an element inside a FormArray, you can use an element index.
+   * For example, to get a `price` control from the first element in an `items` array you can use:
+   *
+   * * `this.form.get('items.0.price');`
+   *
+   * -OR-
+   *
+   * * `this.form.get(['items', 0, 'price']);`
    */
   get(path: Array<string|number>|string): AbstractControl|null {
     return _find(this, path, '.');