This program will not call any of the functions you are implementing, so it does not matter if they are incomplete. It will refuse to build if there are errors present in the `lib.rs`!
Note for trainer: Introduction to the exercise is a guided tour through the template, and it's architecture. Make the participants aware of the placeholders for their implementations. run the hello example on the unmodified lib.
The boards peripherals are represented as nested structs. The `struct Board` contains fields that represent single peripherals or groups of peripherals as structs, which in turn either contain a field of the single peripheral or ...
You have to add structs to represent the buttons and the UARTE peripheral to the board struct.
The `lib.rs` has an attribute #![deny(missing_docs)]. This means, that missing doc comments for structs are returned as compiler errors, to remind you to document your work properly.
Go to [Nordic Infocenter](https://infocenter.nordicsemi.com/topic/ug_nrf52840_dk/UG/dk/intro.html) to download the User Guide. You can find all the information that is relevant to this exercise in there.