add class descriptions.

src/bayesvalidrox/bayes_inference/bayes_inference.py

src/bayesvalidrox/post_processing/post_processing.py

src/bayesvalidrox/pylink/pylink.py

src/bayesvalidrox/surrogate_models/exp_designs.py

src/bayesvalidrox/surrogate_models/inputs.py

src/bayesvalidrox/surrogate_models/sequential_design.py

src/bayesvalidrox/surrogate_models/surrogate_models.py

tests/analytical_function/test_analytical_function.py