Add speaker notes for scopes-shadowing.md

src/basic-syntax/scopes-shadowing.md

@@ -19,3 +19,19 @@ fn main() {
     println!("after: {a}");
 }
 ```
+
+<details>
+
+* Shadowing looks obscure at first, but is convenient for holding on to values after `.unwrap()`.
+* The following code demonstrates why the compiler can't simply reuse memory locations when shadowing an immutable variable in a scope, even if the type does not change.
+
+```rust,editable
+fn main() {
+    let a = 1;
+    let b = &a;
+    let a = a + 1;
+    println!("{a} {b}");
+}
+```
+
+</details>