Category Theory 5.1 - Coproducts sum types

Reposted from [Bartosz Milewski's YouTube channel](https://www.youtube.com/channel/UC8BtBl8PNgd3vWKtm2yJ7aA), with cleaned-up audio. Reposted with permission. See [Republishing Bartosz Milewski's Category Theory lectures](https://www.artificialworlds.net/blog/2021/04/21/republishing-bartosz-milewskis-category-theory-lectures/). You can visit [Bartosz Milewski's Programming Cafe](https://bartoszmilewski.com/) or follow [Bartosz Milewski](https://twitter.com/BartoszMilewski) on Twitter.