Docstring template for our algorithms

[epapoutsellis]

In PR #1030, I introduced the following docstring tempate for the PDHG algorithm:

class MyAlgorithm(Algorithm):

   r""" MyAlgorithm, see :cite:`Add citation`.

   Parameters
   -----------
   Describe all the parameters for the `MyAlgoritm`

  **kwargs
   Describe all the kwargs coming from the base class `Algorithm`

   Example
   --------
   Present a small example

   Notes
   ------
   General information about the algorithm

   Note
   -----
   Describe a general note or a note for a class method, e.g.,

      - The primal objective is printed if `verbose=1`, ``pdhg.run(verbose=1)``.
      - All the objective are printed if `verbose=2`, ``pdhg.run(verbose=2)``.
       Computing these objective can be costly, so it is better to compute every some iterations. To do this, use 
        ``update_objective_interval = #number``.

   References
   -----------

   .. bibliography::   
    """

   def __init__(self):
   """Constructor method
   """

   def set_up(self):
   """Initialisation of the algorithm
   """

   def update(self):
   """ Describe steps for one iteration
   """

In general, I suggest to always show the docs of the update method which basically explains the steps of the algorithm in the optimisation.rst. For the PDHG, it is

.. autoclass:: cil.optimisation.algorithms.PDHG
   :members: update, pdhg_step_sizes, update_step_sizes, update_objective
   :member-order: bysource