correct section link descriptions

doc/src/Section_accelerate.txt

doc/src/Section_commands.txt

doc/src/Section_errors.txt

doc/src/Section_history.txt

doc/src/Section_howto.txt

doc/src/Section_intro.txt

doc/src/Section_modify.txt

doc/src/Section_packages.txt

doc/src/Section_python.txt

doc/src/Section_start.txt

doc/src/accelerate_gpu.txt

doc/src/accelerate_intel.txt

doc/src/accelerate_kokkos.txt

doc/src/accelerate_omp.txt

doc/src/accelerate_opt.txt

doc/src/angle_charmm.txt

doc/src/angle_class2.txt

doc/src/angle_cosine.txt

doc/src/angle_cosine_delta.txt

doc/src/angle_cosine_periodic.txt