Doc/Adding basic usage example in each model docstring #4346

Job	Run time
lint	1m 1s
docs	11m 1s
check-examples (03-FFT-examples.ipynb)	4m 40s
check-examples (04-RNN-examples.ipynb)	10m 9s
check-examples (00-quickstart.ipynb)	8m 10s
check-examples (02-data-processing.ipynb)	9m 48s
check-examples (01-multi-time-series-and-covariates.ipynb)	9m 19s
tests (macos-latest, 3.9, all)	49m 44s
tests (ubuntu-latest, 3.9, all)	46m 15s
	2h 30m 7s

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