Update index.rst with whats new for 2.8 #4986

Job	Run time
pytorch_tutorial_build_worker (1, 15, linux.g5.12xlarge.nvidia.gpu)	14m 25s
pytorch_tutorial_build_worker (3, 15, linux.g5.4xlarge.nvidia.gpu)	23m 38s
pytorch_tutorial_build_worker (4, 15, linux.g5.4xlarge.nvidia.gpu)	30m 37s
pytorch_tutorial_build_worker (5, 15, linux.g5.4xlarge.nvidia.gpu)	22m 29s
pytorch_tutorial_build_worker (2, 15, linux.g5.4xlarge.nvidia.gpu)	38m 41s
pytorch_tutorial_build_worker (9, 15, linux.g5.4xlarge.nvidia.gpu)	19m 20s
pytorch_tutorial_build_worker (13, 15, linux.g5.4xlarge.nvidia.gpu)	15m 22s
pytorch_tutorial_build_worker (12, 15, linux.g5.4xlarge.nvidia.gpu)	15m 40s
pytorch_tutorial_build_worker (7, 15, linux.g5.4xlarge.nvidia.gpu)	23m 5s
pytorch_tutorial_build_worker (10, 15, linux.g5.4xlarge.nvidia.gpu)	16m 55s
pytorch_tutorial_build_worker (14, 15, linux.g5.4xlarge.nvidia.gpu)	28m 41s
pytorch_tutorial_build_worker (11, 15, linux.g5.4xlarge.nvidia.gpu)	14m 7s
pytorch_tutorial_build_worker (6, 15, linux.g5.4xlarge.nvidia.gpu)	26m 59s
pytorch_tutorial_build_worker (8, 15, linux.g5.4xlarge.nvidia.gpu)	9m 33s
pytorch_tutorial_build_worker (15, 15, linux.g5.4xlarge.nvidia.gpu)	19m 4s
pytorch_tutorial_build_manager	0s
	5h 18m 36s

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