It's not possible to share an entire folder yet. It is on our roadmap to encourage team collaboration and folder sharing will be one of those features.
If you'd like, you add that to our product roadmap suggestions page: https://trello.com/b/hQEJSVSQ/loom-roadmap
There you can make a suggestion, vote and comment on other requests, and just follow individual cards to be notified when a particular feature is getting built! It also helps us prioritize our roadmap properly and efficiently.