Show full command in examples

drush migrate-upgrade --help
Perform one or more upgrade processes.

Examples:
  migrate-upgrade --legacy-db-url='mysql://root:pass@127.0.0.1/d6'                  Upgrade a Drupal 6 database to Drupal 8                                             
  migrate-upgrade --legacy-db-key='drupal_7'                                        Upgrade Drupal 7 database where the connection to Drupal 7 has already been created 
                                                                                    in settings.php ($databases['drupal_7'])                                            
  migrate-upgrade --legacy-db-url='mysql://root:pass@127.0.0.1/d7' --configure-only Generate migrations for a custom migration from Drupal 7 to Drupal 8                
 --migration-prefix=d7_custom_ --legacy-root=https://www.example.com       

Currently if you copy/paste code from the examples it won't work because it's not prefixed with drush.

I propose we add drush to the examples as it's done in Drush core commands. Meaning
migrate-upgrade --legacy-db-key='drupal_7' will become drush migrate-upgrade --legacy-db-key='drupal_7'.