Great start on your design docs, here are my notes so far:
MVP LIST
[x] For auth, flesh it out with what features users will have access to when logged in and what they will have access to when logged out. If it's nothing when logged out, be explicit about that.
[x] For each of your MVPs, build out exactly what building the feature will entail. For example, for Discovery Feed, what will users be able to create that will be shown on this feed? Will there be show pages for those things (those things being posts)? Or just the index? Be explicit with each of these MVPs so you have a roadmap as you build your app.
SCHEMA
[x] Yammer requires full name and birthday, so add those as a columns on your users table.
[x] Make sure to include a body on your posts table.
[x] A group can have many users and a user can be in many groups, so you'll need to add a joins table for groups and users.
Great start on your design docs, here are my notes so far: MVP LIST
SCHEMA