Update README to reflect GCP toolkit status

Added a note about GCP being merged into IPC toolkit and repository maintenance status.

Author: Huangzizhou

README.md

@@ -7,7 +7,7 @@
 
 ## Description
 
-GCP toolkit is a set of reusable functions to integrate [Geometric Contact Potential](https://huangzizhou.github.io/research/smooth-contact.html) (GCP) into a simulation, built on top of the [IPC toolkit](https://github.com/ipc-sim/ipc-toolkit).
+GCP toolkit is a set of reusable functions to integrate [Geometric Contact Potential](https://huangzizhou.github.io/research/smooth-contact.html) (GCP) into a simulation, built on top of the [IPC toolkit](https://github.com/ipc-sim/ipc-toolkit). **GCP has been merged into [IPC toolkit](https://github.com/ipc-sim/ipc-toolkit) and this repository is no longer being actively maintained.**
 
 ## Features
 
@@ -31,4 +31,4 @@ This is not a full simulation library. As such it does not include any physics o
 | SmoothCollisionTemplate | EdgeEdgeCollision, FaceVertexCollision, etc. | Specific collision pair type |
 | SmoothCollisionsBuilder | CollisionsBuilder | To construct collision pairs from collision candidates |
 | SmoothCollisions | Collisions | Collection of all collision pairs |
-| SmoothContactPotential | BarrierPotential | Collision potential |
+| SmoothContactPotential | BarrierPotential | Collision potential |