Some docstring refactoring.

4 jobs for field_docu in 6 minutes and 7 seconds (queued for 17 seconds)
Status Name Job ID Coverage
  Test
passed test_min #165271

00:01:37

passed test_mpi #165272

00:03:29

passed test_mpi_fftw #165273

00:03:33

passed test_mpi_fftw_hdf5 #165274

00:05:55

54.0%