Unclear instructions on compatibility mode

[marcushellberg]

The documentation (https://vaadin.com/docs/v14/flow/v14-migration/v14-migration-guide.html) says

Existing Vaadin 10-13 projects can update to 14 without migrating to the new toolset. The only thing that you need to do is to upgrade your Vaadin version to 14.0.0 in your pom.xml. No more changes are needed in your project.

Compatibility mode can be enabled explicitly by including the flow-server-compatibility-mode jar.

This makes it sound like adding the dependency is optional, although it is required.