Add section about panicking.

Author: armandas

src/SUMMARY.md

@@ -6,6 +6,7 @@
   - [Links](./setup/links.md)
 - [Hello World](./hello_world.md)
   - [Delay](./delay.md)
+  - [Panicking](./panicking.md)
   - [Blinky](./blinky.md)
   - [Exercise: working with inputs](./button.md)
 - [Interrupts](./interrupt_intro.md)

src/panicking.md

@@ -0,0 +1,43 @@
+# Panicking
+
+When an unrecoverable error happens in Rust, the program panics.
+There are several ways that panics can be handled, but it usually ends up with your program exiting (crashing).
+
+Let's try it. Add this before the "hello world" message:
+
+```rust
+panic!("Oh no!");
+```
+
+We should observe two things:
+
+1. Compiler gives us "unreachable statement" warning for the code after `panic!()`.
+2. When we run our program, it doesn't appear to do anything.
+
+Let's fix point 2 by displaying the panic information. First, let's import `error` macro from the `log` crate:
+
+```rust
+use log::{info, error};
+```
+
+Then, modify the panic handler, located just after import statements, like so:
+
+1. Give a name to the `PanicInfo` variable. In Rust, we use `_` when we have unused variables that we don't want to name.
+2. Print the panic info using the `error!()` macro.
+
+```rust
+#[panic_handler]
+fn panic(panic_info: &core::panic::PanicInfo) -> ! {
+    error!("{panic_info}");
+    loop {}
+}
+```
+
+Now, we get a useful message about why our program crashed:
+
+```
+ERROR - panicked at src/bin/main.rs:32:9:
+Oh no!
+```
+
+Finally, don't forget to delete the `panic!()` call before proceeding to the next section!