SIRT - documentation unclear for default values for initial

[MargaretDuff]

Description

The documentation suggests that there is a default value for initial

CIL/Wrappers/Python/cil/optimisation/algorithms/SIRT.py

Lines 52 to 64 in eb254e0

	initial : DataContainer, default = None
	Starting point of the algorithm, default value = Zero DataContainer
	operator : LinearOperator
	The operator A.
	data : DataContainer
	The data b.
	lower : :obj:`float`, default = None
	Lower bound constraint
	upper : :obj:`float`, default = None
	Upper bound constraint
	constraint : Function, default = None
	A function with :code:`proximal` method, e.g., :class:`.IndicatorBox` function and :meth:`.IndicatorBox.proximal`,
	or :class:`.TotalVariation` function and :meth:`.TotalVariation.proximal`.

However, the code requires that it is passed:

Environment

import cil, sys
print(cil.version.version, cil.version.commit_hash, sys.version, sys.platform)