how do i add vendor javascript to ember-cli 2.2

This might be a silly question stemming from unfamiliarity. I'm rewriting a project that was previously using Ember 1.7 in Ember 2.3, using Ember-cli v2.2

Now, in the old project, there were a couple of libraries being included manually on the index.html file, put in the scripts directory and then compiled. For example, let's say the JS asset I want to include is offline.js.

I understand that Ember-cli uses Bower and can be used to install bower components, like Bootstrap or moment.js and such. What about custom JS? I've put the file in offline.js, included it in index.html but that doesn't do anything.

I don't think I understand how to add/import vendor assets at all; how do add, say offline.js to the project and have it available throughout the application?