Add marble diagram for Single.repeatUntil operator (#6084)

* Add marble diagram for Single.repeatUntil operator

* Use proper URL for marble

Author: UMFsimke

src/main/java/io/reactivex/Single.java

@@ -3119,6 +3119,8 @@ public final Flowable<T> repeatWhen(Function<? super Flowable<Object>, ? extends
 
     /**
      * Re-subscribes to the current Single until the given BooleanSupplier returns true.
+     * <p>
+     * <img width="640" height="463" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Single.repeatUntil.png" alt="">
      * <dl>
      *  <dt><b>Backpressure:</b></dt>
      *  <dd>The returned {@code Flowable} honors the backpressure of the downstream consumer.</dd>