Add a comment on drawer layout file.

Bug: 9075592
Change-Id: I839d54ccf4a4eb82e30798408927759da247cde9
diff --git a/samples/Support4Demos/res/layout/drawer_layout.xml b/samples/Support4Demos/res/layout/drawer_layout.xml
index 375c802..496bd88 100644
--- a/samples/Support4Demos/res/layout/drawer_layout.xml
+++ b/samples/Support4Demos/res/layout/drawer_layout.xml
@@ -24,7 +24,8 @@
     android:layout_width="match_parent"
     android:layout_height="match_parent">
     <!-- As the main content view, the view below consumes the entire
-         space available using match_parent in both dimensions. -->
+         space available using match_parent in both dimensions. Note that
+         this child does not specify android:layout_gravity attribute. -->
     <ScrollView
         android:layout_width="match_parent"
         android:layout_height="match_parent"