Detach fork from Crater invoice

[rihards-simanovics]

I just accidentally made a pull request into the crater-invoice docs repo instead of to our own docs repo, as GitHub by default directs PRs to the upstream repo, not the one from which the fork was made.

@Darko, we need to detach from the crater-invoice/docs repo, as we are now an independent project.

[gdarko]

I requested it @rihards-simanovics