Need to reorganize / edit "Managing Dependencies" section

[Gaurav0]

I don't think this belongs in "writing addons" because this is mostly about importing and customizing dependencies which can either be done in the app via ember-cli-build.js or in the addon via index.js. How exactly it should be organized probably deserves further discussion on discord. There is a discussion about this on Discord here: https://discordapp.com/channels/480462759797063690/480777444203429888/499943437626507274

See also my review here: #19 (review)

[BradenLawrence]

Thanks for reviewing and adding this issue! I can pick up a few of the items you called out:

• "Mention it will use yarn when there is both a yarn.lock and a package-lock.json"
• "It should be not recommended to use bower. It is not officially deprecated, but it should be."
• "but does not watch node_modules."
  I'll add any followup questions inline with your review.

[jenweber]

Proposed breakdown:

Basic Use - Importing Assets
Advanced Use - Managing Dependencies
Writing Addons - Including Assets In Addons

Copied from Gaurav's comments on #24

[jenweber]

Closed by #40