Rename extensions to anchors

docs/configuration/overview.md

@@ -16,15 +16,15 @@ e.g., `kamal deploy -d staging`.
 In this case, the configuration will also be read from `config/deploy.staging.yml`
 and merged with the base configuration.
 
-## [Extensions](#extensions)
+## [Anchors](#anchors)
 
 Kamal will not accept unrecognized keys in the configuration file.
 
 However, you might want to declare a configuration block using YAML anchors
 and aliases to avoid repetition.
 
 You can prefix a configuration section with `x-` to indicate that it is an
-extension. Kamal will ignore the extension and not raise an error.
+anchor. Kamal will ignore the anchor and not raise an error. See [Anchors](../anchors) for more information.
 
 ## [The service name](#the-service-name)