clarify the hidden APIs in reference with better tooltips

Change-Id: Iaa843b4a0462195084fb7a35e826eeec92d50c64
diff --git a/tools/droiddoc/templates-sdk/assets/js/docs.js b/tools/droiddoc/templates-sdk/assets/js/docs.js
index 8c00da7..1996dac 100644
--- a/tools/droiddoc/templates-sdk/assets/js/docs.js
+++ b/tools/droiddoc/templates-sdk/assets/js/docs.js
@@ -2382,7 +2382,8 @@
     // Grey things out that aren't available and give a tooltip title
     if (apiLevelNum > selectedLevelNum) {
       obj.addClass("absent").attr("title","Requires API Level \""
-            + apiLevel + "\" or higher");
+            + apiLevel + "\" or higher. To reveal, change the target API level "
+              + "above the left navigation.");
     }
     else obj.removeClass("absent").removeAttr("title");
   });