Clarify usage of #[interrupt] attribute and recommend device crate re…

[HosseinAssaran]

…-export

[BartMassey]

Thanks much for this! The text is a definite improvement. I wonder why the code needed to change?

Any chance you could do a similar PR for https://github.com/rust-embedded/discovery-mb2

[HosseinAssaran]

It demonstrates how to use interrupts and highlights the need to include use device::interrupt. Additionally, since the emulator in this book is based on the LM3S6965, which does not have a TIM2 peripheral but instead provides TIMER2A and TIMER2B, the code must be adapted accordingly.

[therealprof]

LGTM