title: How to configure Doctrine to use yaml mapping on Symfony 4
body: <p>I'm new to Symfony <strong>4</strong></p>
  
  <p>I use Doctrine an I want to use <strong>yaml</strong> entity mapping.
  So i configured the file <code>doctrine.yaml</code> and change <code>type:annotation</code> to <code>type:yml</code>.</p>
  
  <p>And when I tried <code>php bin/console make:entity</code>, there is no yaml mapping file generated linked to this entity</p>
  
  <p>this is my <code>doctrine.yaml</code> file:</p>
  
  <pre>
  parameters:
      # Adds a fallback DATABASE_URL if the env var is not set.
      # This allows you to run cache:warmup even if your
      # environment variables are not available yet.
      # You should not need to change this value.
      env(DATABASE_URL): ''
  
  doctrine:
      dbal:
          # configure these for your database server
          driver: 'pdo_mysql'
          server_version: '5.7'
          charset: utf8mb4
  
          # With Symfony 3.3, remove the `resolve:` prefix
          url: '%env(resolve:DATABASE_URL)%'
      orm:
          auto_generate_proxy_classes: '%kernel.debug%'
          naming_strategy: doctrine.orm.naming_strategy.underscore
          auto_mapping: true
          mappings:
              App:
                  is_bundle: false
                  type: yml
                  dir: '%kernel.project_dir%/src/Entity'
                  prefix: 'App\Entity'
                  alias: App
  </pre>