Need to update with SIV support in mind

[pkieltyka]

SIV was introduced after docgen, so we need to account now for the project path when generating import paths.

I'm too busy and wont have time for this, but if someone wants to tackle it, im happy to review a PR

[micheartin]

What is SIV?

[micheartin]

Ah! After some search I have finally found the motivation: https://github.com/golang/go/issues/44550 I understand better the requirements. Not easy…