The advice when such questions are asked is almost always to get a lawyer. But maybe if you think it is a frivolous lawsuit you can reach out to the EFF for help?
Thanks. I've considered the EFF, but their criteria for taking on cases prioritizes cases that have a broad impact on the internet and privacy. I guess emailing them couldn't hurt. Maybe I could consider getting investments to fund the legal costs.
Primptly contact the EFF for advice on finding a lawyer, yes. Your lawyer's initial advice may be to take down the docs for the time being. Your lawyer is likely to then send them a letter asking them to explain "with specificity" (those are magic words) exactly what part of your project is infringing and how it can be modified to not infringe.