Provide reference documentation for transform parameters

[dstansby]

The Image Registration Optimizer Weights example says:

we use the SetOptimizerWeights method to disable rotations around the x and y axes

SetOptimizerWeights takes an interable of weights that correspond to parameters of the Transform, but it is currently not possible to understand from the API reference what order the transform parameters are listed in.

For example, for SimilarityTransform3D I think the order is [3 versor componets, 3 translation components, isotropic scale factor], but looking at the API reference for SimilarityTransform3D there is no way to learn this. It would be great if the parameters that each transform takes were listed in the API reference.

[blowekamp]

Generally lower level information is in the ITK level documentation: https://itk.org/Doxygen/html/classitk_1_1Similarity3DTransform.html "The serialization of the optimizable parameters is an array of 7 elements. The first 3 elements are the components of the versor representation of 3D rotation. The next 3 parameters defines the translation in each dimension. The last parameter defines the isotropic scaling."

But I think it is reasonable to add that information to the SImpleITK documentation.