thelio-mira-r5-n4: Add usage note for USB4

[jklgrasso]

Originally:

Using two high bandwidth devices (eGPU, USB4 dock, etc.) on both USB4 ports may limit port capability/device functionality. We recommend connecting only one high bandwidth USB4 device to the system at a time. Some USB4 devices may not work correctly if connected _after_ powering the system on.

@jacobgkau refined the original into bullet points 😄

[jacobgkau]

Seems like @thomas-zimmerman is on-board, too, based on the Slack reaction.