Update README: note fork origin, summarize changes, remove PWC badge.

README.md

@@ -81,7 +81,7 @@ model-index:
 
 # SparseBEV
 
-[![PWC](https://img.shields.io/endpoint.svg?url=https://paperswithcode.com/badge/sparsebev-high-performance-sparse-3d-object/3d-object-detection-on-nuscenes-camera-only)](https://paperswithcode.com/sota/3d-object-detection-on-nuscenes-camera-only?p=sparsebev-high-performance-sparse-3d-object)
+This is a fork of [MCG-NJU/SparseBEV](https://github.com/MCG-NJU/SparseBEV) with modifications to add ONNX export support targeting Apple Silicon via ONNX Runtime's CoreML Execution Provider. [See the full description of changes below.](#changes-from-upstream)
 
 This is the official PyTorch implementation for our ICCV 2023 paper: