v4 page for spacy.io

[danieldk]

Description

I have put this in draft, because it still needs careful review.

Types of change

Docs

Checklist

• I confirm that I have the right to submit this contribution under the project's MIT license.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.