This HTML file is located on the MICROBIT drive. It is locked and so cannot be edited. The file contains information about the micro:bit, including the board ID number and interface version (described in DETAILS.TXT)
For example, the file may contain a link such as
https://microbit.org/device/?id=9904&v=0255
This link currently directs you to the user guide on the microbit.org website, but could be used in future to provide specific guidance on the board or the firmware that is being used.