Boot time reduction - Wire.setClock(400000)

[rtek1000]

The GSL1680 managed to work in my tests with more than 400kHz, so it may be interesting to add this instruction to the code.

GSL1680.cpp

    Wire.begin();
    
    Wire.setClock(400000); // 4x faster than standard 100 kHz

[Skallwar]

Nice, good find. I think it's a parameter that depend on both GSL1680 and the board used so I'm not sure this should be added to the driver itself but it could be a great addition to the README.md