add: recommended image sizes

[LPX55]

[vercel[bot]]

@LPX55 is attempting to deploy a commit to the 1hive Team on Vercel.

A member of the Team first needs to authorize it.

[vercel[bot]]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://vercel.com/1hive/gardens-ui/D4dXpzdWut75mqyiVMLdncekLhoM
✅ Preview: https://gardens-ui-git-fork-lpx55-lpx-dw-10fixonboarding-specify-1hive.vercel.app

[LPX55]

gm! Please let me know if I understood the scope of this properly or if I missed something.

I guesstimated the recommended sizes by looking at existing gardens and seeing how the images are displayed. I haven't found an official recommended size, but if there were official sizes that are recommended I can make the changes.