Create specific category for tablets on doc.e.foundation/devices

Summary

Create a product category for tablets, next to smartphones and laptops.

What is the current behavior?

We support tablets with /e/OS, but they are buried with smartphones and there is no easy way to list these models

What is the improved behavior?

There should be a specific category for tablets.

What does it bring?

More users for /e/OS on a tablet. More clarity about supported tablets.

Install /e/OS on a tablet.