Update addons / libraries / dependencies documentation to better represent the current state of npm support

[NullVoxPopuli]

Motivation is so that devs just quick skimming the this page: https://guides.emberjs.com/v3.24.0/addons-and-dependencies/
don't feel like they need to install broccoli transform addons and do app.import for every dependency.

This is the only mention that I could find/skim of how things actually work

Based on conversations in Discord lately,
I think the page should be more like:

• explain what can go in the browser and what can't (node vs module/browser and how package.json plays in to that)
• some common things people might want to do with ember-auto-import
• much later down in the page, explain advanced stuff / legacy things (the current stuff)

[jenweber]

This page could definitely be improved! Contributors are welcome to make big changes or small changes in their PRs. One thing that needs to stay the same is that we cannot remove existing headings. Sections can be moved around, and we can add new headings. This is so that we don't break anyone's bookmarks or blog links.

Contributors should only edit the page found in the release directory, and not older guides versions.

This ticket is related to #1559