updated edit-view-zones.png to show new alignment field, and added explanantory

text to README

README.md

@@ -11,6 +11,7 @@ The editor is fully guided. Features include:
 * custom zone labels
 * ability to show or hide zone borders
 * custom text and background colors for items
+* optional auto-alignment for items (left, right, center)
 * image items
 * items prompting for additional (numerical) input after being dropped
 * decoy items that don't have a zone
@@ -102,7 +103,7 @@ above the background image, the introductory feedback (shown
 initially), and the final feedback (shown after the learner
 successfully completes the drag and drop problem).
 
-![Drop zone edit](https://raw.githubusercontent.com/edx-solutions/xblock-drag-and-drop-v2/c955a38dc3a1aaf609c586d293ce19b282e11ffd/doc/img/edit-view-zones.png)
+![Drop zone edit](https://raw.githubusercontent.com/edx-solutions/xblock-drag-and-drop-v2/7bb3fa837764af8f58129093df85ff6845a927c0/doc/img/edit-view-zones.png)
 
 In the next step, you set the URL and description for the background
 image and define the properties of the drop zones. For each zone you
@@ -114,6 +115,16 @@ whether or not to display borders outlining the zones. It is possible
 to define an arbitrary number of drop zones as long as their labels
 are unique.
 
+Additionally, you can specify the alignment for items once they are dropped in
+the zone.  No alignment is the default, and causes items to stay where the
+learner drops them.  Left alignment causes dropped items to be placed from left
+to right across the zone. Right alignment causes the items to be placed from
+right to left across the zone. Center alignment places items from top to bottom
+along the center of the zone. If left, right, or center alignment is chosen,
+items dropped in a zone will not overlap, but if the zone is not made large
+enough for all its items, they will overflow the bottom of the zone, and
+potentially, overlap the zones below.
+
 ![Drag item edit](https://raw.githubusercontent.com/edx-solutions/xblock-drag-and-drop-v2/c955a38dc3a1aaf609c586d293ce19b282e11ffd/doc/img/edit-view-items.png)
 
 In the final step, you define the background and text color for drag