Add openvino export and supported models sections #766

Job	Run time
build (3.8, optimum, ubuntu-22.04)	30m 21s
build (3.8, optimum, windows-latest)	58m 29s
build (3.8, git+https://github.com/huggingface/optimum.git, ubuntu-22.04)	33m 10s
build (3.8, git+https://github.com/huggingface/optimum.git, windows-latest)	56m 31s
build (3.12, optimum, ubuntu-22.04)	31m 30s
build (3.12, optimum, windows-latest)	46m 54s
build (3.12, git+https://github.com/huggingface/optimum.git, ubuntu-22.04)	36m 15s
build (3.12, git+https://github.com/huggingface/optimum.git, windows-latest)	47m 13s
	5h 40m 23s

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