weights of some custom datasets

1. logo. mAP@IoU0.5 = 0.736
2. birdview_vehicles. mAP@IoU0.5 = 0.761

pretrained_weight_pytorch_20200723

1.2

update D7X description on readme

custom dataset for tutorial

1. simple shapes
2. logo
3. birdview_vehicles

pretrained_weights_pytorch_20200406

these weights are tested