Adding Debug instructions to README.md

[evildaemond]

Adding some lines to the README.md file to assist with debugging, turns out SD Cards suck...

### Debugging

The `sdCommand(): Card Failed! cmd: 0x00` error appears when the Micro SD does not connect to the ESP32

1. Check to make sure the Micro SD Card is installed
1. Using the continuity test on a Multimeter, verify if all traces are soldered properly

In the event of an error log which shows `sdcard_mount(): f_mount failed: (3) The physical drive cannot work`,

1. Make sure your Micro SD Card is formatted to FAT32
1. Check the Micro SD Card is suitable (Some forms of SanDisk SD cards such as the 32gb range will silently fail with this error)