mention memoise package in chapter 1.6 - objects that take a long time to create?

[david-barnett]

Thanks for creating this book/resource, I have certainly learned some great tips from it, and frequently refer others here :)

To me, chapter 1.6 seems like a relevant place to mention memoisation as one solution to speeding up end-to-end code reruns? https://rstats.wtf/save-source.html#objects-that-take-a-long-time-to-create