Make zero-shot automl more discoverable

[sonichi]

1. Shall we insert cross-links in the two notebooks https://github.com/microsoft/FLAML/blob/main/notebook/automl_lightgbm.ipynb and https://github.com/microsoft/FLAML/blob/main/notebook/zeroshot_lightgbm.ipynb to make the zero-shot automl more discoverable?
2. Shall we insert links in lightgbm's documentation page to tuning and zero-shot examples respectively?

@mkyl @qingyun-wu @liususan091219