[css-scroll-snap] Fix broken image links

Author: ChumpChief

css-scroll-snap/Overview.bs

@@ -114,7 +114,7 @@ Motivating Examples {#examples}
         </pre>
 
         <figure>
-            <img src="element_snap_positions.png" alt="">
+            <img src="images/element_snap_positions.png" alt="">
 
             <figcaption>
                 The layout of the scroll container's contents in the example.
@@ -159,7 +159,7 @@ Motivating Examples {#examples}
         </pre>
 
         <figure>
-            <img src="element_snap_positions_offset.png" alt="">
+            <img src="images/element_snap_positions_offset.png" alt="">
 
             <figcaption>
                 The layout of the scroll container's contents in the example.