Add README to references/segmentation (#1864)

references/segmentation/README.md

+# Semantic segmentation reference training scripts
+
+This folder contains reference training scripts for semantic segmentation.
+They serve as a log of how to train specific models, as provide baseline
+training and evaluation scripts to quickly bootstrap research.
+
+All models have been trained on 8x V100 GPUs.
+
+## fcn_resnet101
+```
+python -m torch.distributed.launch --nproc_per_node=8 --use_env train.py --lr 0.02 --dataset coco -b 4 --model fcn_resnet101 --aux-loss
+```
+
+## deeplabv3_resnet101
+```
+python -m torch.distributed.launch --nproc_per_node=8 --use_env train.py --lr 0.02 --dataset coco -b 4 --model deeplabv3_resnet101 --aux-loss
+```