docs(focal): make gutenberg/zola relation more prominent

[janbrasna]

🎉 Thanks for submitting a pull request! 🎉

Summary

Refs netlify/binrc#35

Zola is the new name for Gutenberg (and @keats/gutenberg redirects to @getzola/zola).

So binaries <=0.4 were referred to and cached as gutenberg. Versions >=0.5 and later are available as zola.

As the effort to alias aliases and manage similar renames is probably not worth it, just a nod in a direction there has been a change in names at some point in the projects history should be enough to hint people tripping over something where to look to adjust things…

(Not sure if it's worth cherry-picking to xenial docs too?)

(Originally came here to fix Gutenberg spelling. Since it's been superseded by Zola anyways this makes more sense.)

---

For us to review and ship your PR efficiently, please perform the following steps:

• [x] Read the contribution guidelines 📖. This ensures your code follows our style guide and passes our tests.
• [x] Update the included software doc (if you updated included software) 📄
• [x] Update or add documentation (if features were changed or added) 📝
• [ ] Make sure the status checks below are successful ✅

A picture of a cute animal (not mandatory, but encouraged)