Add comments about the type specific Model::add####() methods and relation to Component::addComponent().
Add comments about the type specific Model::add####() methods and relation to Component::addComponent().

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