Add new section on trait bounds.

exercises/04_traits/05_trait_bounds/Cargo.toml

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+[package]
+name = "trait_bounds"
+version = "0.1.0"
+edition = "2021"

exercises/04_traits/05_trait_bounds/src/lib.rs

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+// TODO: Add the necessary trait bounds to `min` so that it compiles successfully.
+//   Refer to `std::cmp` for more information on the traits you might need.
+//
+// Note: there are different trait bounds that'll make the compiler happy, but they come with
+// different _semantics_. We'll cover those differences later in the course when we talk about ordered
+// collections (e.g. BTreeMap).
+
+/// Return the minimum of two values.
+pub fn min<T>(left: T, right: T) -> T {
+    if left <= right {
+        left
+    } else {
+        right
+    }
+}