feat: showcasing example of adding and holding a reference to a vector

Signed-off-by: Fredrik Klingenberg <fredrkl@gmail.com>

projects/collections/src/main.rs

@@ -9,4 +9,15 @@ fn main() {
     v.push(6);
     v.push(7);
     v.push(8);
+
+    let e = vec![1, 2, 3, 4, 5];
+    let third = &e[2];
+    // e.push(6); // Changing e to mutable (mut) and uncommenting this line will cause an error because we are trying to borrow a mutable reference to e while we have an immutable reference to e
+    println!("The third element is {}", third);
+
+    let third = e.get(2); // The reson why this is option is because it might not exist, the index might be out of bounds
+    match third {
+        Some(third) => println!("The third element is {}", third),
+        None => println!("There is no third element"),
+    }
 }