book: view_code update for xtask

Author: AfoHT

book/en/src/by-example/tips/view_code.md

@@ -1,8 +1,29 @@
 # Inspecting generated code
 
-`#[rtic::app]` is a procedural macro that produces support code. If for some reason you need to inspect the code generated by this macro you have two options:
+`#[rtic::app]` is a procedural macro that produces support code.
+If for some reason you need to inspect the code generated by this macro you have two options:
 
-You can inspect the file `rtic-expansion.rs` inside the `target` directory. This file contains the expansion of the `#[rtic::app]` item (not your whole program!) of the *last built* (via `cargo build` or `cargo check`) RTIC application. The expanded code is not pretty printed by default, so you'll want to run `rustfmt` on it before you read it.
+* You can inspect the file `rtic-expansion.rs` inside the `target` directory.
+* Use the [`cargo-expand`] sub-command
+
+## Using generated `rtic-expansion.rs`
+
+Locating this file depends on how building is performed.
+
+Using e.g. `cargo xtask build-example` within the main RTIC repo will place the file based on "platform" used:
+```
+$ cargo xtask example-build --example smallest
+$ cargo xtask example-build --example monotonic --platform esp32-c3
+
+$ fd -u rtic-expansion.rs
+examples/esp32c3/target/rtic-expansion.rs
+examples/lm3s6965/target/rtic-expansion.rs
+```
+
+In the regular cargo project case it goes directly in the `target` folder.
+
+This file contains the expansion of the `#[rtic::app]` item (not your whole program!) of the *last built* (via `cargo build` or `cargo check`) RTIC application.
+The expanded code is not pretty printed by default, so you'll want to run `rustfmt` on it before you read it.
 
 ``` console
 $ cargo build --example smallest --target thumbv7m-none-eabi
@@ -34,7 +55,16 @@ mod app {
 }
 ```
 
-Or, you can use the [`cargo-expand`] sub-command. This sub-command will expand *all* the macros, including the `#[rtic::app]` attribute, and modules in your crate and print the output to the console.
+## Using `cargo-expand` tool
+
+If not available, install:
+
+```
+$ cargo install cargo-expand
+```
+
+This sub-command will expand *all* the macros, including the `#[rtic::app]` attribute, and modules in your crate and print the output to the console.
+
 
 [`cargo-expand`]: https://crates.io/crates/cargo-expand