Adding W&B (wandb) experiment tracking (#304)

.gitignore

README.md

docs/images/wandb_screenshot.png

scripts/spellcheck_conf/wordlist.txt

src/llama_recipes/configs/__init__.py

src/llama_recipes/configs/training.py

src/llama_recipes/configs/wandb.py

src/llama_recipes/finetuning.py

src/llama_recipes/utils/train_utils.py