config: clarify the "bottom-most" verbiage

Because stacks

Signed-off-by: Vincent Batts <[email protected]>

Author: vbatts

config.md

@@ -143,12 +143,12 @@ Since the configuration JSON that gets hashed references hashes of each layer in
 
     - **diff_ids** *array*, REQUIRED
 
-       An array of layer content hashes (`DiffIDs`), in order from bottom-most to top-most.
+       An array of layer content hashes (`DiffIDs`), in stack order from bottom-most to top-most (i.e. from `diff_ids[0]` to `diff_ids[len(diff_ids)]`).
 
 - **history** *array of objects*, OPTIONAL
 
   Describes the history of each layer.
-  The array is ordered from bottom-most layer to top-most layer.
+  The array is stack ordered from bottom-most layer to top-most layer.
   The object has the following fields:
 
     - **created** *string*, OPTIONAL