Add some specific documentation for uploading files

[jrjohnson]

Uploading files with an event is a specific code path and the task can
be tough to figure out without an example.

I couldn't think of a better way to document this, but it seemed necessary to me. I've been using a construct like:

inputElement.triggerHandler({
 type: 'change',
 target: {
  files: {
   0: file,
   length: 1,
   item() { return file; }
  }
 }
});

So when converting from jQuery helpers to this addon it was difficult to see how to make file uploads work. Turns out some really nice work is done in fire-event.js - just needed to be documented.

[jrjohnson]

I'm assuming these test failures have nothing to do with this doc change.

[Turbo87]

The API docs are automatically generated, so you would have to change this in the JS docs, not in the API docs directly.

[jrjohnson]

Whoops. Thanks @Turbo87. I fixed that, it doesn't like like docs get built in Travis so I assume I was supposed to commit the change to API.md as well?

I had to add *'s to the docs. Otherwise the whitespace was stripped from the example.

[ro0gr]

a minor indentation issue, this bracket should be moved one char left

[jrjohnson]

Thanks @ro0gr. Fixed.

[jrjohnson]

@Turbo87 / @ro0gr just wanted to check in. Is this something worth merging? I'm ok with closing it un-merged if it isn't.

[rwjblue]

Yes! Absolutely!

[rwjblue]

Thank you!