Clarify that default reconciliation configs are built-in

Users can override defaults or define configs for other plugins,
but cannot customize the built-in defaults themselves.

Author: cowwoc

src/site/markdown/how-to.md

@@ -174,9 +174,8 @@ projects where compiler version changes can cause compilation failures.
 **Important:** When you explicitly configure `executionControl` for a plugin, your explicit configuration completely overrides
 the defaults for that plugin. However, defaults still apply to other plugins that aren't explicitly configured.
 
-**Customizing Defaults:** To add additional default reconciliation configs, create a `default-reconciliation/defaults.xml` file
-in your classpath following the schema in `default-reconciliation.xsd`. This allows projects to define their own defaults without
-modifying the build cache extension.
+**Extending Beyond Defaults:** You can define reconciliation configurations for plugins that don't have built-in defaults by
+adding them to your `executionControl` configuration as shown in the examples above.
 
 ### Parameter Validation and Categorization