Developing addons audit

Overall, I think the tutorial has most of the import topics covered but I think `isDevelopingAddon` should be mentioned as you won't see live reloads in your linked app if you make changes to the addon

Developers are used to seeing the reloads when working on regular ember apps.

Second, it's not part of old cli docs but should we mention ember-cli-github-pages as a way to deploy to gh-pages, similar to the way ember-cli-addon-docs is mentioned?

I can do a PR if there is agreement