Adding a small explanations on hardware exceptions vs software exceptions

[Dajamante]

In the book there is a paragraph on hardware exceptions:
https://docs.rust-embedded.org/book/start/exceptions.html?highlight=exception#the-default-exception-handler
This can be a question mark for people used to software exceptions.

What about adding, directly after the first paragraph:

Hardware exceptions are different from exceptions thrown in software, which are a way of handling errors for both recoverable and unrecoverable errors. For recoverable error handling, Rust uses the Result type Result<T, E>, where T is the Ok value type, and E is a specific, configurable error. For unrecoverable software error handling, Rust uses panic that stops execution. This is closer to exceptions thrown in software using other languages.

If you think it can be a useful addition I can make a PR.