docs: update register map spreadsheet

[silaswaxter]

• Clarify bits in the CALIBRATION_REQUEST register.
  • The cell for bit 3 is marked as reserved, but the comment clearly states that this bit is used for collecting data for accel/fine-mag calibration in the current orientation. Upon reading other sources of documentation (hackaday blog and original USFSMAX repo's README), its clear that this function is used during manufacturing calibration of the device. I suggest adding this to the comment and pointing users to supporting documentation for more info.
• Specify the type of DHI_RSQ in the name of the register. Perhaps pseudofloat.
  • From the ESP32's sketch void USFSMAX::getDHI_Rsq() , the resultant type is a float, but the received int16_t is a fixed-point number with an implicit scaling factor of 10000.
• Add reset values registers
• Add documentation for configuration structures to spreadsheet.

[silaswaxter]

I checked off these tasks because its clear that this register map is not a standalone document, and one must read the sketch example code to interpret types. The other 2 bullet points would be nice though.