Updating the docs around node.js version

[twokul]

Currently, we support only node@6+ (mostly b/c of the way we wrote the blueprint). For example,

// ember-cli-build.js
const { GlimmerApp } = require('@glimmer/application-pipeline');

Destructuring is not supported in 4.

related to glimmerjs/glimmer-vm#579

[rwjblue]

Hmm. We should probably make another issue to actually fix node@4 support. We do intend to follow the same policy as ember-cli itself RE: node support (which means all supported node LTS's and "current release").

[locks]

I was thinking the same but forgot to follow through 👍

[twokul]

@rwjblue I think it makes perfect sense but we don't want to alienate people b/c of wrong docs and it seemed like a quicker fix than to fix bluerprint

[rwjblue]

Ya, totally agree with the change here for the interim. I'm just saying we should also try to fix Node 4.

[locks]

See the referenced issue above ;)