Update CHANGES.md

Installation/CHANGES.md

@@ -3,6 +3,10 @@
 
 ## [Release 6.1](https://github.com/CGAL/cgal/releases/tag/v6.1)
 
+### [Polygon Mesh Processing](https://doc.cgal.org/6.1/Manual/packages.html#PkgPolygonMeshProcessing)
+- Added the function `CGAL::Polygon_mesh_processing::discrete_mean_curvature` and `CGAL::Polygon_mesh_processing::discrete_Guassian_curvature` to evaluate the discrete curvature at a vertex of a mesh.
+- Added the function `CGAL::Polygon_mesh_processing::angle_sum` to compute the sum of the angles around a vertex.
+
 ### [Algebraic Kernel](https://doc.cgal.org/6.1/Manual/packages.html#PkgAlgebraicKernelD)
 
 -   **Breaking change**: Classes based on the RS Library are no longer provided.