Clean up E0522 explanation

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0522.md

@@ -1,7 +1,5 @@
-The lang attribute is intended for marking special items that are built-in to
-Rust itself. This includes special traits (like `Copy` and `Sized`) that affect
-how the compiler behaves, as well as special functions that may be automatically
-invoked (such as the handler for out-of-bounds accesses when indexing a slice).
+The lang attribute was used in an invalid context.
+
 Erroneous code example:
 
 ```compile_fail,E0522
@@ -12,3 +10,8 @@ fn cookie() -> ! { // error: definition of an unknown language item: `cookie`
     loop {}
 }
 ```
+
+The lang attribute is intended for marking special items that are built-in to
+Rust itself. This includes special traits (like `Copy` and `Sized`) that affect
+how the compiler behaves, as well as special functions that may be automatically
+invoked (such as the handler for out-of-bounds accesses when indexing a slice).