[algorithms][num_segments] add doxy/qbk documentation

include/boost/geometry/algorithms/num_segments.hpp

@@ -232,6 +232,17 @@ struct num_segments<boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)> >
 
 
 
+/*!
+\brief \brief_calc{number of segments}
+\ingroup num_segments
+\details \details_calc{num_segments, number of segments}.
+\tparam Geometry \tparam_geometry
+\param geometry \param_geometry
+\param add_for_open add one for open geometries (i.e. polygon types which are not closed)
+\return \return_calc{number of segments}
+
+\qbk{[include reference/algorithms/num_segments.qbk]}
+*/
 template <typename Geometry>
 inline std::size_t num_segments(Geometry const& geometry,
                                 bool add_for_open = false)