Update docs/5.x upgrade guide.md

Co-authored-by: Nick Grosenbacher <nickgrosenbacher@gmail.com>

docs/5.x upgrade guide.md

@@ -52,7 +52,7 @@ Some of the most notable changes are:
 - The new `TemplatesType`, `ArrayFieldDescriptionProps`, `ArrayFieldTitleProps`, `UnsupportedFieldProps`, `IconButtonProps`, `SubmitButtonProps` and `UIOptionsBaseType` were added to support the consolidation (and expansion) of `templates` in the `Registry` and `Form`.
 - **BREAKING CHANGE** The `DescriptionField` and `TitleField` props were removed from the `ArrayFieldTemplateProps` and `ObjectFieldTemplateProps` as they can now be derived from the `templates` or `uiSchema` via the new `getTemplate()` utility function.
 - **BREAKING CHANGE** The `fields` prop was removed from the `FieldTemplateProps` as you can simply use `registry.fields` instead.
-- **BREAKING CHANGE** The `showErrorList` prop was changed to accept `top` or `bottom`.
+- **BREAKING CHANGE** The `showErrorList` prop was changed to accept `false`, `"top"` or `"bottom"`. `true` is no longer a valid value. The default value is `"top"`, which has identical behavior to the default value/`true` in v4.
 You can view all these [types](https://github.com/rjsf-team/react-jsonschema-form/blob/main/packages/utils/src/types.ts) on Github.
 
 #### Form props