Observers working with Spoonfeeder

What works now:

1. Install the migrations like in the new `README.md`
2. Install it in the Spoonfeeder app and run it with `rails s`
3. Create some posts and comments
4. Nothing more is implemented, but you can see that activities (or `Carriages`) have been created by:
5. Entering the console with `rails c`.
6. Running `ChooChoo::Carriage.all` which gives you a list of all created activities.