Fix ddev integration

With the MR ddev composer install works

ddev composer install                           
Installing dependencies from lock file (including require-dev)
Verifying lock file contents can be installed on current platform.
Nothing to install, update or remove
Generating autoload files
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However I still get an error on ddev install

ddev install         
PHP Fatal error:  Uncaught AssertionError: assert($this->bootstrap instanceof DrupalBoot8) in /var/www/html/vendor/drush/drush/src/Boot/BootstrapManager.php:119
Stack trace:
#0 /var/www/html/vendor/drush/drush/src/Boot/BootstrapManager.php(119): assert()
#1 /var/www/html/vendor/drush/drush/src/Boot/BootstrapManager.php(108): Drush\Boot\BootstrapManager->bootstrap()
#2 /var/www/html/vendor/drush/drush/src/Application.php(165): Drush\Boot\BootstrapManager->setUri()
#3 /var/www/html/vendor/drush/drush/src/Runtime/Runtime.php(97): Drush\Application->refineUriSelection()
#4 /var/www/html/vendor/drush/drush/src/Runtime/Runtime.php(40): Drush\Runtime\Runtime->doRun()
#5 /var/www/html/vendor/drush/drush/drush.php(140): Drush\Runtime\Runtime->run()
#6 /var/www/html/vendor/bin/drush.php(119): include('...')
#7 {main}
  thrown in /var/www/html/vendor/drush/drush/src/Boot/BootstrapManager.php on line 119

I should have read the README. This works fine

ddev poser
ddev symlink-project
ddev install

We could put guard rails in like if drush is not installed say maybe you haven't run

ddev poser
ddev symlink-project

ddev symlink-project is supposed to run automatically on start, but I feel it doesn't, but all it does is symlink the project into web/modules/custom