NXP backend: Update user guide and docs Readme #10139

Job	Run time
gather-models	10s
test-models-linux (buck2, mv3, portable, linux.2xlarge, 90) / linux-job	9m 0s
test-models-linux (cmake, vit, portable, linux.2xlarge, 90) / linux-job	16m 6s
test-models-linux (buck2, mv3, xnnpack-quantization-delegation, linux.2xlarge, 90) / linux-job	10m 4s
test-models-linux (cmake, vit, xnnpack-quantization-delegation, linux.2xlarge, 90) / linux-job	11m 9s
test-models-linux (cmake, mv3, xnnpack-quantization-delegation, linux.2xlarge, 90) / linux-job	9m 16s
test-models-linux (cmake, mv3, portable, linux.2xlarge, 90) / linux-job	8m 56s
	1h 4m 41s

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