Add examples of the super learner

[zhizuio]

Add some examples of the super learner. See the new tutorial and it illustrated code:

• Ruth Keogh, Karla Diaz-Ordaz, Nan van Geloven, Jon Michael Gran, Kamaryn Tanner (2025). The super learner for time-to-event outcomes: A tutorial. arXiv:2509.03315.

• Code for reproducing the data analysis in the tutorial: https://github.com/ruthkeogh/superlearner_survival_tutorial.git