book: Add note to remember to choose target
@@ -53,6 +53,10 @@ $ cargo run --example init
{{#include ../../../../ci/expected/init.run}}
```
+> **NOTE**: Remember to always specify your chosen target device or configure
+> one to be used by default in `.cargo/config.toml`. In this case, we use
+> a Cortex M3 running in QEMU so the target is `thumbv7m-none-eabi`.
+
## `idle`
A function marked with the `idle` attribute can optionally appear in the
