Document table columns preference

docs/development/user-preferences.md

@@ -8,3 +8,4 @@ The `users.UserConfig` model holds individual preferences for each user in the f
 | ---- | ----------- |
 | extras.configcontext.format | Preferred format when rendering config context data (JSON or YAML) |
 | pagination.per_page | The number of items to display per page of a paginated table |
+| tables.${table_name}.columns | The ordered list of columns to display when viewing the table |