FYI, USAGE.md seems to be missing.
Also, a suggestion: while I agree with other posters that this isn't a replacement for the third-party trust model DocuSign provides, you might as well use my OpenTimestamps project to timestamp the documents OpenSign produces. Being able to prove that a document was in fact created in the past, before a dispute existed about the document, is significantly better than not being able to prove that. OpenTimestamps is free and open source, using Bitcoin so that you don't have a trusted third party. Timestamps made with OpenTimestamps are free, as merkle trees are used to allow the whole world's documents to be timestamped with a single Bitcoin transaction.
A good example of how it's been used recently is by the official election authority in Guatemala to timestamp polling documents in their recent presidential election: https://www.youtube.com/watch?v=g0nnM5_Z90E