Continuous integration section

• [x] scikit-ci: https://github.com/scikit-build/scikit-ci
• [x] scikit-ci-addons: https://github.com/scikit-build/scikit-ci-addons
• [ ] Multibuild - https://github.com/matthew-brett/multibuild

scikit-ci and scikit-ci-addons are referenced from Bonus Exercise 4: Setting up continuous integration in Binaries and Dependencies section.