Update future plan section in README.md

Author: zitongzhan

README.md

@@ -79,6 +79,7 @@
 
 ### Future Plan
 - [ ] Add Apple Silicon GPU support, [PyTorch PR WIP](https://github.com/pytorch/pytorch/pull/177757)
+- [ ] Schur complement
 - [ ] Reduce runtime overhead using CUDA graph
 - [ ] Distributed Tensor (DTensor) support
 - [ ] An new backend for [distributed solver](https://github.com/NVIDIA/AMGX)