message: Add display function in file format doc
diff: File formats
  ############
  -To find the correct function to read the files, please refer to :doc:`reader_utils_ref`
  -
  Persistence Diagram
  *******************
  -Such a file, whose extension is usually ``.pers``, contains a list of persistence intervals.
  +Such a file, whose extension is usually ``.pers``, contains a list of
  +persistence intervals.
  Lines starting with ``#`` are ignored (comments).
  -Other lines might contain 2, 3 or 4 values (the number of values on each line must be the same for all lines)::
  +Other lines might contain 2, 3 or 4 values (the number of values on each line
  +must be the same for all lines)::
  [[field] dimension] birth death
  @@ -25,6 +25,9 @@ Here is a simple sample file::
  Other sample files can be found in the data/persistence_diagram folder.
  -Such files can be generated with :meth:`gudhi.SimplexTree.write_persistence_diagram` and read with
  +Such files can be generated with
  +:meth:`gudhi.SimplexTree.write_persistence_diagram`, read with
  :meth:`gudhi.read_persistence_intervals_grouped_by_dimension`, or
  -:meth:`gudhi.read_persistence_intervals_in_dimension`.
  +:meth:`gudhi.read_persistence_intervals_in_dimension` and displayed with
  +:meth:`gudhi.plot_persistence_barcode` or
  +:meth:`gudhi.plot_persistence_diagram`.
  