Clarify documentation of permission to restore changes

The 'Abandon' access permission also grants permission to restore
changes, but this is only effective if the user also has push
permission for the change's destination ref.

Clarify this in the documentation.

Change-Id: Ib35250dee8aa8d8a0c2138d5b9be09ad7245e655
diff --git a/Documentation/access-control.txt b/Documentation/access-control.txt
index 5102033..9ff0156 100644
--- a/Documentation/access-control.txt
+++ b/Documentation/access-control.txt
@@ -419,8 +419,9 @@
 to projects in Gerrit. It can give permission to abandon a specific
 change to a given ref.
 
-This also grants the permission to restore a change if the change
-can be uploaded.
+This also grants the permission to restore a change if the user also
+has link:#category_push[push permission] on the change's destination
+ref.
 
 
 [[category_create]]