Documentation code example not working

[Shotman]

After following the example code in the README this is not working on symfony 4 or 5.
I get an error "cannot call method createForm on null", this I've noticed it can be fixed by adding a constructor in the DynamicFormAware trait like this
public function __construct() { $this->dynamicFormFactory = new FormFactory(); }
but then I get an error that the key "new_user" is not found, so I don't know where the form yaml should be put.

Could you update the doc and/or the bundle please ?