Initial commit: DCNv4 custom op mirror setup

- Add enhanced README with project structure and quick start guide
- Initialize repository with DCNv4 CUDA extension (PyTorch module)
- Include classification, detection, and segmentation subdirectories
- Reference upstream OpenGVLab DCNv4 implementation

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

detection/dist_train.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+CONFIG=$1
+GPUS=$2
+PORT=${PORT:-29500}
+# cat /proc/193481/cmdline
+PYTHONPATH="$(dirname $0)/..":$PYTHONPATH \
+python -m torch.distributed.launch --nproc_per_node=$GPUS --master_port=63667 \
+    $(dirname "$0")/train.py $CONFIG --launcher pytorch ${@:3}