Update index.rst with whats new for 2.8 #5019

Job	Run time
pytorch_tutorial_build_worker (6, 15, linux.g5.4xlarge.nvidia.gpu)	26m 59s
pytorch_tutorial_build_worker (10, 15, linux.g5.4xlarge.nvidia.gpu)	28m 56s
pytorch_tutorial_build_worker (1, 15, linux.g5.12xlarge.nvidia.gpu)	14m 42s
pytorch_tutorial_build_worker (4, 15, linux.g5.4xlarge.nvidia.gpu)	28m 4s
pytorch_tutorial_build_worker (5, 15, linux.g5.4xlarge.nvidia.gpu)	22m 25s
pytorch_tutorial_build_worker (8, 15, linux.g5.4xlarge.nvidia.gpu)	24m 13s
pytorch_tutorial_build_worker (2, 15, linux.g5.4xlarge.nvidia.gpu)	24m 7s
pytorch_tutorial_build_worker (12, 15, linux.g5.4xlarge.nvidia.gpu)	15m 26s
pytorch_tutorial_build_worker (7, 15, linux.g5.4xlarge.nvidia.gpu)	28m 52s
pytorch_tutorial_build_worker (11, 15, linux.g5.4xlarge.nvidia.gpu)	13m 55s
pytorch_tutorial_build_worker (9, 15, linux.g5.4xlarge.nvidia.gpu)	19m 2s
pytorch_tutorial_build_worker (15, 15, linux.g5.4xlarge.nvidia.gpu)	18m 48s
pytorch_tutorial_build_worker (14, 15, linux.g5.4xlarge.nvidia.gpu)	27m 29s
pytorch_tutorial_build_worker (3, 15, linux.g5.4xlarge.nvidia.gpu)	24m 25s
pytorch_tutorial_build_worker (13, 15, linux.g5.4xlarge.nvidia.gpu)	14m 57s
pytorch_tutorial_build_manager	1s
	5h 32m 21s

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