Fix and improve new methods API documentation

Signed-off-by: Gabriel Pacheco <gabriel.fpacheco@gmail.com>

include/gz/sim/Link.hh

@@ -362,18 +362,18 @@ namespace gz
       /// collision shapes attached to the it. The link bounding box is
       /// generated by merging all the bounding boxes of the collision
       /// geometries.
-      /// \param _ecm
+      /// \param[in] _ecm Entity-component manager.
       /// \return Link's axis-aligned bounding box in the link frame or
-      /// nullopt if the link does not have collisions. It may return an
-      /// empty bounding box if all of the link collisions are empty.
+      /// nullopt if the link does not have collisions. It returns an
+      /// invalid bounding box if all of the link collisions are empty.
       public: std::optional<math::AxisAlignedBox> AxisAlignedBox(
           const EntityComponentManager &_ecm) const;
 
       /// \brief Get the link's axis-aligned bounding box in the world frame
-      /// \param _ecm Entity-component manager.
+      /// \param[in] _ecm Entity-component manager.
       /// \return Link's axis-aligned bounding box in the world frame or
-      /// nullopt if the link does not have collisions. It may return an
-      /// empty bounding box if all of the link collisions are empty.
+      /// nullopt if the link does not have collisions. It returns an
+      /// invalid bounding box if all of the link collisions are empty.
       /// \sa AxisAlignedBox
       public: std::optional<math::AxisAlignedBox> WorldAxisAlignedBox(
           const EntityComponentManager &_ecm) const;