microbit: Added details for the i2c silicone glitch
microbit: Added details for the i2c silicone glitch

As per https://github.com/lancaster-university/microbit-dal/issues/83 the comment in the MicroBitI2c.h file lacked context around a known hardware glitch. This commit rectifies this issue by adding a link to a collection PDF providing a more detailed explanation.
markshannon/microbit-dal,markshannon/microbit-dal