docs: Noted that JobIntentService is usually a better choice

Since IntentService is subject to the O background restrictions,
most devs are better off switching to the new JobIntentService.
(I assume IntentService is not actually deprecated; if it is, tell
me and I'll change this to a @deprecated tag!)

See first comment for doc stage location.

Test: make ds-docs
Bug: 64159987
Change-Id: I83a53d1e6336c2134bf4c61bedd2ae42cd80493a
diff --git a/core/java/android/app/IntentService.java b/core/java/android/app/IntentService.java
index e4a22c4..95ec24c 100644
--- a/core/java/android/app/IntentService.java
+++ b/core/java/android/app/IntentService.java
@@ -43,6 +43,13 @@
  * long as necessary (and will not block the application's main loop), but
  * only one request will be processed at a time.
  *
+ * <p class="note"><b>Note:</b> IntentService is subject to all the
+ * <a href="/preview/features/background.html">background execution limits</a>
+ * imposed with Android 8.0 (API level 26). In most cases, you are better off
+ * using {@link android.support.v4.app.JobIntentService}, which uses jobs
+ * instead of services when running on Android 8.0 or higher.
+ * </p>
+ *
  * <div class="special reference">
  * <h3>Developer Guides</h3>
  * <p>For a detailed discussion about how to create services, read the
@@ -50,6 +57,7 @@
  * guide.</p>
  * </div>
  *
+ * @see android.support.v4.app.JobIntentService
  * @see android.os.AsyncTask
  */
 public abstract class IntentService extends Service {