Depend on ember-cli-rails 1.x

[tricknotes]

Why

#42 declares a dependency on ember-cli-rails without naming a version, because the release it needs is not published yet.
This names it: ~> 1.0, so only the 1.x series is accepted.

No published release works with the helpers of #42, which was checked against every release from 0.13.0 on:

• none of 0.13.0, 0.13.1, 0.13.2, 0.14.0, 0.14.1 or 0.14.2 expose vite?, startup_tags, javascript_assets or stylesheet_assets on EmberCli::App.
  Paired with 0.14.2, every example in spec/helpers fails with the EmberCli::App class does not implement the instance method: vite?
• each of those releases also depends on ember-cli-rails-assets >= 0.9.0, < 1.0, so Bundler rejects the pair outright: Your bundle requires gems that depend on each other, creating an infinite loop.

1.0.0 is the release that both adds those readers and drops the dependency back on this gem, so it is the oldest one that can work.
The upper bound keeps out the next major release, which is free to change what the helpers read.

What

• s.add_dependency "ember-cli-rails", "~> 1.0", replacing the comment that deferred it
• The README and the CHANGELOG entry name the 1.x series

Merging

Merge this once ember-cli-rails 1.0.0 is published.

Until then, CI fails at bundle install: the Gemfile resolves ember-cli-rails from the branch of tricknotes/ember-cli-rails#687, whose version is still 0.14.2, which ~> 1.0 does not accept.
When 1.0.0 is published, that Gemfile line comes out and ember-cli-rails resolves from RubyGems.