Simplify the example code for Clone (#2001)

The previous example code for the `Clone` slide was a bit too complex in
a way that obscured the fundamental point. I've replaced it with the
`say_hello` example from the previous slide, but updated to demonstrate
how cloning can address the borrow checker error. I also added a speaker
note to mention that `Clone` performs a deep copy, which might be
different from what students are used to if they come from a language
like Python that does shallow copies by default.

src/memory-management/clone.md

@@ -8,26 +8,29 @@ Sometimes you _want_ to make a copy of a value. The `Clone` trait accomplishes
 this.
 
 ```rust,editable
-#[derive(Default)]
+fn say_hello(name: String) {
-struct Backends {
+    println!("Hello {name}")
-    hostnames: Vec<String>,
-    weights: Vec<f64>,
 }
 
-impl Backends {
+fn main() {
-    fn set_hostnames(&mut self, hostnames: &Vec<String>) {
+    let name = String::from("Alice");
-        self.hostnames = hostnames.clone();
+    say_hello(name.clone());
-        self.weights = hostnames.iter().map(|_| 1.0).collect();
+    say_hello(name);
-    }
 }
 ```
 
 <details>
 
-The idea of `Clone` is to make it easy to spot where heap allocations are
+- The idea of `Clone` is to make it easy to spot where heap allocations are
-occurring. Look for `.clone()` and a few others like `Vec::new` or `Box::new`.
+  occurring. Look for `.clone()` and a few others like `Vec::new` or `Box::new`.
 
-It's common to "clone your way out" of problems with the borrow checker, and
+- It's common to "clone your way out" of problems with the borrow checker, and
-return later to try to optimize those clones away.
+  return later to try to optimize those clones away.
+
+- `clone` generally performs a deep copy of the value, meaning that if you e.g.
+  clone an array, all of the elements of the array are cloned as well.
+
+- The behavior for `clone` is user-defined, so it can perform custom cloning
+  logic if needed.
 
 </details>