Hi wkh,
Our documentation team is working to make these documents available through our website. In the meanwhile, I have made them available here:
https://github.com/knightsifive/SiFive-Learn-Inventor-Docs
This includes the FE310-G003 manual and datasheet, the SiFive Learn Inventor schematics, and the SiFive Learn Inventor Getting Started Guide.
Best,
Nick Knight
Technical Lead, Software Performance Team
EDIT: I have taken down this link because some of the documents were incomplete and our team is working to fix them.