docs: improved local setup instructions?

[bshaffer]

In order to install the fixtures, I ran bin/console doctrine:fixtures:load and received the error Invalid fallback user was not found:

 Careful, database "packagist" will be purged. Do you want to continue? (yes/no) [no]:
 > yes

   > purging database
   > loading App\DataFixtures\UserFixtures
   > loading App\DataFixtures\PackageFixtures
  0/100 [>---------------------------]   0% (< 1 sec left) https://github.com/php-fig/log16:30:57 INFO      [app] Updating 
16:30:57 CRITICAL  [console] Error thrown while running command "doctrine:fixtures:load -v". Message: "Invalid fallback user was not found" ["exception" => LogicException { …},"command" => "doctrine:fixtures:load -v","message" => "Invalid fallback user was not found"]

In UpdaterWorker.php line 160:
                                       
  [LogicException]                     
  Invalid fallback user was not found  
                                       
Exception trace:
  at packagist/src/Service/UpdaterWorker.php:160
 App\Service\UpdaterWorker->process() at packagist/src/DataFixtures/PackageFixtures.php:101
 App\DataFixtures\PackageFixtures->updatePackage() at packagist/src/DataFixtures/PackageFixtures.php:82
 App\DataFixtures\PackageFixtures->load() at packagist/vendor/doctrine/data-fixtures/src/Executor/AbstractExecutor.php:122
 Doctrine\Common\DataFixtures\Executor\AbstractExecutor->load() at packagist/vendor/doctrine/data-fixtures/src/Executor/ORMExecutor.php:26
 Doctrine\Common\DataFixtures\Executor\ORMExecutor::Doctrine\Common\DataFixtures\Executor\{closure}() at packagist/vendor/doctrine/orm/src/EntityManager.php:272
 Doctrine\ORM\EntityManager->wrapInTransaction() at packagist/vendor/doctrine/data-fixtures/src/Executor/ORMExecutor.php:20
 Doctrine\Common\DataFixtures\Executor\ORMExecutor->execute() at packagist/vendor/doctrine/doctrine-fixtures-bundle/src/Command/LoadDataFixturesDoctrineCommand.php:140
 Doctrine\Bundle\FixturesBundle\Command\LoadDataFixturesDoctrineCommand->doExecute() at packagist/vendor/doctrine/doctrine-fixtures-bundle/src/Command/CommandCompatibility.php:18
 Doctrine\Bundle\FixturesBundle\Command\LoadDataFixturesDoctrineCommand->execute() at packagist/vendor/symfony/console/Command/Command.php:279
 Symfony\Component\Console\Command\Command->run() at packagist/vendor/symfony/console/Application.php:1047
 Symfony\Component\Console\Application->doRunCommand() at packagist/vendor/symfony/framework-bundle/Console/Application.php:123
 Symfony\Bundle\FrameworkBundle\Console\Application->doRunCommand() at packagist/vendor/symfony/console/Application.php:316
 Symfony\Component\Console\Application->doRun() at packagist/vendor/symfony/framework-bundle/Console/Application.php:77
 Symfony\Bundle\FrameworkBundle\Console\Application->doRun() at packagist/vendor/symfony/console/Application.php:167
 Symfony\Component\Console\Application->run() at packagist/vendor/symfony/runtime/Runner/Symfony/ConsoleApplicationRunner.php:49
 Symfony\Component\Runtime\Runner\Symfony\ConsoleApplicationRunner->run() at packagist/vendor/autoload_runtime.php:29

So I decided to comment out the use of Seldaek in fallback_gh_tokens in config/parameters.yaml, but then I received the error "Email " does not comply with addr-spec of RFC 2822.

So I set the env var APP_MAILER_FROM_EMAIL in .env, but then I received the error Environment variable not found: "APP_DEV_EMAIL_RECIPIENT"`.

After setting that environment variable, I finally ended with the error Integrity constraint violation: 1062 Duplicate entry '' for key 'package.package_name_idx', and decided to come here for help.

I am just trying to load the fixtures in the dev environment, so I am not sure why it needs to find a "invalid fallback user" in the User database to do that. I am thinking this must be a bug.