Suggest to chose fp16 or bf16 configuration for fine-tuning to match the same as the training of the model

[kjappelbaum]

closed via #137

[kjappelbaum]

The corresponding precisions are also logged here https://docs.google.com/spreadsheets/d/14vbBbuRMEHoqeuMHkTfw3uiZVmyXNuoSp8s-aHvfvZk/edit?gid=0#gid=0 besides the HF wiki

[kjappelbaum]

let's add a reference to that (so that this book also stays a useful resource for us ;))