Swap of Ch4 and Ch5 incomplete

[d-s-d]

There is a note in Ch5 that now refers to pattern matching being introduced in «[...] in a later chapter [...]»—however, it is now introduced in Ch4. Also, the code examples would need to be updated accordingly; i.e. use pattern matching instead of if/else.

Stupid question: what is the best way to contribute here?

[Zelenya]

Oh, my bad, thank you for catching these. Opening Pull Request with changes would be very helpful, see the Contribution guide for instructions. Let us know if you have any other questions