docs(skipUntil): add example with an interval waiting for click (#4696)

src/internal/operators/skipUntil.ts

@@ -10,8 +10,35 @@ import { Subscription } from '../Subscription';
 /**
  * Returns an Observable that skips items emitted by the source Observable until a second Observable emits an item.
  *
+ * The `skipUntil` operator causes the observable stream to skip the emission of values ​​until the passed in observable emits the first value.
+ * This can be particularly useful in combination with user interactions, responses of http requests or waiting for specific times to pass by.
+ *
  * ![](skipUntil.png)
  *
+ * Internally the `skipUntil` operator subscribes to the passed in observable (in the following called *notifier*) in order to recognize the emission
+ * of its first value. When this happens, the operator unsubscribes from the *notifier* and starts emitting the values of the *source*
+ * observable. It will never let the *source* observable emit any values if the *notifier* completes or throws an error without emitting
+ * a value before.
+ *
+ * ## Example
+ *
+ * In the following example, all emitted values ​​of the interval observable are skipped until the user clicks anywhere within the page.
+ *
+ * ```ts
+ * import { interval, fromEvent } from 'rxjs';
+ * import { skipUntil } from 'rxjs/operators';
+ *
+ * const intervalObservable = interval(1000);
+ * const click = fromEvent(document, 'click');
+ *
+ * const emitAfterClick = intervalObservable.pipe(
+ *   skipUntil(click)
+ * );
+ * // clicked at 4.6s. output: 5...6...7...8........ or
+ * // clicked at 7.3s. output: 8...9...10..11.......
+ * const subscribe = emitAfterClick.subscribe(value => console.log(value));
+ * ```
+ *
  * @param {Observable} notifier - The second Observable that has to emit an item before the source Observable's elements begin to
  * be mirrored by the resulting Observable.
  * @return {Observable<T>} An Observable that skips items from the source Observable until the second Observable emits