Documentation should explain where to get firmware files

[jms1voalte]

Missing feature

https://mooltipass.github.io/minible/updating_your_device.html explains how to UPLOAD a bundle file, but it doesn't explain how or where to GET a bundle file.

Also, at the moment bundle 13 doesn't seem to be available through the https://www.themooltipass.com/updates/ page, when I enter 12 as the current bundle number it says that version is too high.

Justification

The documentation should explain how/where to get the update files.

Workarounds

If the files from the releases list can be used to upgrade an MPBLE, this should be explained as well. As far as I've ever known, the only files that can/should be used to upgrade the hardware are the serial-specific files available through the updates page.