We've been using Database Note Taker to document our sql server databases. It's easy to set up and easy for team members to share their documentation notes - in a single or multiple files which we pop in source control so we have a record of those. We prefer the documentation to be separate to the actual database. We don't need the relationships because those are obvious - we just need notes for what each field does and this tool does it. And we can see what's been documented and what has not so a developer can easily see what needs attention if they have spare time. Plus is publishes to a html page we can use our own xml stylesheet to customise that and we can easily send that to customers or print to pdf. Too easy.