Move example closer to explaination

#1120 (comment)

Author: XrXr

src/items/associated-items.md

@@ -296,6 +296,22 @@ type. It is written the same as a [constant item].
 Unlike [free] constants, associated constant definitions undergo
 [constant evaluation] only when referenced.
 
+```rust
+struct Struct;
+
+impl Struct {
+    const ID: i32 = 1;
+    // Definition not immediately evaluated
+    const PANIC: () = panic!("compile-time panic");
+}
+
+fn main() {
+    assert_eq!(1, Struct::ID);
+    // Referencing Struct::PANIC causes compilation error
+    // let _ = Struct::PANIC;
+}
+```
+
 ### Associated Constants Examples
 
 A basic example:
@@ -338,24 +354,6 @@ fn main() {
 }
 ```
 
-[Constant evaluation] timing:
-
-```rust
-struct Struct;
-
-impl Struct {
-    const ID: i32 = 1;
-    // Definition not immediately evaluated
-    const PANIC: () = panic!("compile-time panic");
-}
-
-fn main() {
-    assert_eq!(1, Struct::ID);
-    // Referencing Struct::PANIC causes compilation error
-    // let _ = Struct::PANIC;
-}
-```
-
 [_ConstantItem_]: constant-items.md
 [_Function_]: functions.md
 [_MacroInvocationSemi_]: ../macros.md#macro-invocation