changed description in the MarkerPlacer header filer (test)
changed description in the MarkerPlacer header filer (test)

opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core