centerPoint enhanced & DEMsystem modified for id

- center points enhanced to select particle ids based on the particles located in box, sphere and cylinder
- readme.md modified
- DEMsystem is modified to pass id

DEMSystems/sphereDEMSystem/sphereDEMSystem.hpp

@@ -63,6 +63,8 @@ protected:
 
 	ViewType1D<real, HostSpace> 	diameterHost_;
 
+	ViewType1D<uint32, HostSpace> 	particleIdHost_;
+
 	bool 							requireRVel_ = false;
 
 	ViewType1D<realx3, HostSpace> 	rVelocityHost_;
@@ -122,6 +124,8 @@ public:
 
 	span<const int32> parIndexInDomain(int32 di)const override;
 
+	span<uint32> particleId() override;
+
 	span<real> diameter() override;
 
 	span<real> courseGrainFactor() override;