DOC Add explanation for default values

src/Model/Blog.php

@@ -120,6 +120,8 @@ class Blog extends Page implements PermissionProvider
     ];
 
     /**
+     * The ProvideComments db column is defined in the silverstripe/comments module
+     *
      * @var array
      */
     private static $defaults = [

src/Model/BlogPost.php

@@ -100,6 +100,9 @@ class BlogPost extends Page
     ];
 
     /**
+     * The ProvideComments db column is defined in the silverstripe/comments module
+     * The InheritSideBar db column is defined in the silverstripe/widgets module
+     *
      * @var array
      */
     private static $defaults = [