Document USB Hub usage

According to @eric.kuzmenko, who tested a USB-C hub with his dev kit having most of the high-current loads disabled, some USB-C hubs may require the dev kit to have an 18650 battery inserted (one that meets the specs we've outlined).

We should document this when documenting a "desktop like" setup.

Edited Mar 07, 2019 by Eric Kuzmenko

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