generics1 rewrite and solution

solutions/14_generics/generics1.rs

@@ -1 +1,17 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+// `Vec<T>` is generic over the type `T`. In most cases, the compiler is able to
+// infer `T`, for example after pushing a value with a concrete type to the vector.
+// But in this exercise, the compiler needs some help through a type annotation.
+
+fn main() {
+    // `u8` and `i8` can both be converted to `i16`.
+    let mut numbers: Vec<i16> = Vec::new();
+    //             ^^^^^^^^^^ added
+
+    // Don't change the lines below.
+    let n1: u8 = 42;
+    numbers.push(n1.into());
+    let n2: i8 = -1;
+    numbers.push(n2.into());
+
+    println!("{numbers:?}");
+}