Add pre-req on lmp device registration page

[kprosise]

Added an "important" admonition to the top of the page, clarifying that the device must be running the LmP first.

Checked rendered output and links. No issues found.

This commit addresses FFTK-4733, "Add note to device registration…"

PR Template and Checklist

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[angolini]

Instead of doing this change, why now add a "landing page" for device registration where you can access two tabs with how to register in the two different ways?