role 'hetznerbackup' was not found

[fuchsi3010]

hi, thanks for this playbook!
i've tried to use this by :

1. cloning the repo to my local machine
2. editing the variables in hosts.yml
3. generating & copying a rsa key to the hetzner-storagebox
4. editing playbook.yml and finally
5. running ansible-playbook -i hosts.yml playbook.yml.

i'm getting the error:

ERROR! the role 'hetznerbackup' was not found in /home/$USER/ansible/hetznerbackup/roles:/home/$USER.ansible/roles:/usr/share/ansible/roles:/etc/ansible/roles:/home/$USER/ansible/hetznerbackup

The error appears to be in '/home/$USER/ansible/hetznerbackup/playbook.yml': line 8, column 7, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:

  roles:
    - hetznerbackup
      ^ here

i'm new to ansible, could be obvious what i'm missing, but i'm stuck at this point. any help/advice would be great!
PS: do i need to edit defaults/main.yml at all?
thanks!