add README.md about Migrating between strategies.

Command/MigrateNamingStrategyCommand.php

@@ -5,10 +5,9 @@
 
 use Arxy\FilesBundle\Manager;
 use Arxy\FilesBundle\Model\File;
+use Arxy\FilesBundle\NamingStrategy;
 use Doctrine\Common\Persistence\ManagerRegistry;
-use Psr\Container\ContainerInterface;
 use Symfony\Component\Console\Command\Command;
-use Symfony\Component\Console\Input\InputArgument;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Style\SymfonyStyle;
@@ -19,25 +18,18 @@ class MigrateNamingStrategyCommand extends Command
 
     private Manager $fileManager;
     private ManagerRegistry $doctrine;
-    private ContainerInterface $container;
+    private NamingStrategy $oldNamingStrategy;
 
-    public function __construct(Manager $fileManager, ManagerRegistry $registry, ContainerInterface $container)
+    public function __construct(Manager $fileManager, ManagerRegistry $registry, NamingStrategy $oldNamingStrategy)
     {
         parent::__construct();
         $this->fileManager = $fileManager;
         $this->doctrine = $registry;
-        $this->container = $container;
-    }
-
-    protected function configure()
-    {
-        $this->addArgument('old-naming-strategy', InputArgument::REQUIRED);
+        $this->oldNamingStrategy = $oldNamingStrategy;
     }
 
     protected function execute(InputInterface $input, OutputInterface $output)
     {
-        $oldNamingStrategy = $this->container->get($input->getArgument('old-naming-strategy'));
-
         $io = new SymfonyStyle($input, $output);
         $progressBar = $io->createProgressBar();
 
@@ -54,7 +46,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
             /** @var File $file */
             $file = $row[0];
 
-            $migrated = $this->fileManager->migrate($file, $oldNamingStrategy);
+            $migrated = $this->fileManager->migrate($file, $this->oldNamingStrategy);
             if ($migrated) {
                 $totalMigrated++;
                 $io->success('File '.$file->getId().' migrated');

README.md

@@ -446,4 +446,24 @@ You will receive following json as response:
       "squared_thumbnail":"https:\/\/host.com\/media\/cache\/resolve\/squared_thumbnail\/1\/4\/5\/145"
    }
 }
-```
+```
+
+## Migrating between naming strategy.
+
+First configure the new naming strategy, but keep the old one as service.
+Then register the command for migration:
+```yaml
+services:
+    Arxy\FilesBundle\Command\MigrateNamingStrategyCommand:
+        arguments:
+            $oldNamingStrategy: 'old_naming_strategy_service_id'
+```
+
+then run it. 
+```shell script
+bin/console arxy:files:migrate-naming-strategy
+```
+
+Please note that until files are migrated - if some file is requested - it will throw error.
+
+