Notify the user when their 32-bit computer won't work with Tails 3.0

Let’s make this notification point to the blog post that will result from #12192 (closed).

This branch shall be reverted on feature/stretch, where its only effect would be to eat memory and CPU cycles.

Feature Branch: feature/12193-notify-if-32-bit

Original created by @intrigeri on 12193 (Redmine)

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