Fix broken link in prototype_index (#3360) #4419

Job	Run time
pytorch_tutorial_build_worker (2, 15, linux.g5.4xlarge.nvidia.gpu)	37m 43s
pytorch_tutorial_build_worker (12, 15, linux.g5.4xlarge.nvidia.gpu)	21m 21s
pytorch_tutorial_build_worker (10, 15, linux.g5.4xlarge.nvidia.gpu)	16m 32s
pytorch_tutorial_build_worker (13, 15, linux.g5.4xlarge.nvidia.gpu)	27m 45s
pytorch_tutorial_build_worker (11, 15, linux.g5.4xlarge.nvidia.gpu)	15m 48s
pytorch_tutorial_build_worker (7, 15, linux.g5.4xlarge.nvidia.gpu)	17m 53s
pytorch_tutorial_build_worker (4, 15, linux.g5.4xlarge.nvidia.gpu)	33m 52s
pytorch_tutorial_build_worker (6, 15, linux.g5.4xlarge.nvidia.gpu)	22m 42s
pytorch_tutorial_build_worker (8, 15, linux.g5.4xlarge.nvidia.gpu)	22m 49s
pytorch_tutorial_build_worker (15, 15, linux.g5.4xlarge.nvidia.gpu)	28m 52s
pytorch_tutorial_build_worker (1, 15, linux.g5.12xlarge.nvidia.gpu)	15m 18s
pytorch_tutorial_build_worker (3, 15, linux.g5.4xlarge.nvidia.gpu)	22m 18s
pytorch_tutorial_build_worker (9, 15, linux.g5.4xlarge.nvidia.gpu)	18m 7s
pytorch_tutorial_build_worker (14, 15, linux.g5.4xlarge.nvidia.gpu)	26m 48s
pytorch_tutorial_build_worker (5, 15, linux.g5.4xlarge.nvidia.gpu)	23m 39s
pytorch_tutorial_build_manager	22m 31s
	6h 13m 58s

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