The user manual PDF thoroughly documents the best collaboration process in §5.3.2, under subheading, Merging Projects Together, starting on page 75. The basic technique is described, and tips for collaboration are given, starting on page 78. Here are some discussions referring to this approach in a more brief, summary manner:
- Multi-user cross platform use by collaborators
- Seeking advice about cross-platform collaboration
- Collaboration Workflow for Spousal Writing
And here are some older threads on the topic. If you aren’t comfortable with the more modern “import and merge” approach, or are on Windows with both machines and do not have that feature yet, then the following advice will help. All you need is one Mac to operate as the “host” though. The Windows version is fully compatible with the workflow, it just lacks the actual merging/sync technology.
Some prefer this approach anyway, you just have to be way more careful about it since you don’t want two people opening the project at once. With Import and Merge, both people can work at the same time and sync their independent changes together on a regular basis.