Generator: add comment on why we inherit from G4 instead of APSQ

    /**

     * @brief Initializer for the generator actions, required for \ref RunManager

     *

     * We directly inherit from Geant4's action initialization class instead of the DepositionGeant4 class since the latter

     * provides functionality specific to that module which we do not need - while we need to be able to pass an additional

     * parameter, the PrimariesReader, to the action constructor.

     */

    template <class GEN> class ActionInitializationPrimaries : public G4VUserActionInitialization {

    public:

        explicit ActionInitializationPrimaries(const Configuration& config, std::shared_ptr<PrimariesReader> reader)

            : config_(config), reader_(std::move(reader)){};

            : config_(config), reader_(reader){};

        /**

         * @brief Build the user action to be executed by the worker