Clean up error codes E0223 and E0225 explanations

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0223.md

@@ -1,5 +1,6 @@
 An attempt was made to retrieve an associated type, but the type was ambiguous.
-For example:
+
+Erroneous code example:
 
 ```compile_fail,E0223
 trait MyTrait {type X; }

src/librustc_error_codes/error_codes/E0225.md

@@ -1,12 +1,15 @@
-You attempted to use multiple types as bounds for a closure or trait object.
-Rust does not currently support this. A simple example that causes this error:
+Multiple types were used as bounds for a closure or trait object.
+
+Erroneous code example:
 
 ```compile_fail,E0225
 fn main() {
     let _: Box<dyn std::io::Read + std::io::Write>;
 }
 ```
 
+Rust does not currently support this.
+
 Auto traits such as Send and Sync are an exception to this rule:
 It's possible to have bounds of one non-builtin trait, plus any number of
 auto traits. For example, the following compiles correctly: