Add three more sentences about what Octane is to the Octane page

We should add 2-3 quick "marketing" focused sentences directly to the Octane page, at the very beginning.

To-do:

- [ ] draft additions/edits for the `octane` page, using some of the feedback and suggestions below. These are rough suggestions so it's up to you to figure out wording.
- [ ] check to see if messaging is consistent with `editions/index` and the [upgrading section](https://octane-guides-preview.emberjs.com/release/upgrading/editions/) of the Octane guides preview
- [ ] If there are inconsistencies, include changes to `editions` in the same PR, and open an issue in the Guides for the Upgrading page. Link to it here.

Feedback from @chriskrycho:

I'm thinking something very roughly like:

- Modern JavaScript, with ES6 classes, decorators, async/await, and zero-config npm interop
- A lighter-weight component API, including syntax for better readability
- No need for jQuery, legacy classes (.extend() and .create() etc.), or computed properties

I shared https://emberjs.com/editions/octane/ with some folks, and a dev who really likes Ember but has been doing other stuff for the last couple years looked at it and wrote: "That page doesn't seem to explain what Ember Octane is"

It seems like we probably need something like a super condensed version of https://octane-guides-preview.emberjs.com/release/upgrading/editions/ and the Roadmap on that page, just for pure marketing reasons, presumably with links to more details.
Is there any place we have a short summary of "Here's what's new!"? Like https://octane-guides-preview.emberjs.com/release/upgrading/editions/#toc_features-overview, I guess?