Rollup merge of #74977 - GuillaumeGomez:cleanup-e0741, r=pickfire

Clean up E0741 error explanation

r? @Dylan-DPC

Author: Manishearth

src/librustc_error_codes/error_codes/E0741.md

@@ -1,5 +1,6 @@
-Only structural-match types (that is, types that derive `PartialEq` and `Eq`)
-may be used as the types of const generic parameters.
+A non-structural-match type was used as the type of a const generic parameter.
+
+Erroneous code example:
 
 ```compile_fail,E0741
 #![feature(const_generics)]
@@ -9,12 +10,15 @@ struct A;
 struct B<const X: A>; // error!
 ```
 
-To fix this example, we derive `PartialEq` and `Eq`.
+Only structural-match types (that is, types that derive `PartialEq` and `Eq`)
+may be used as the types of const generic parameters.
+
+To fix the previous code example, we derive `PartialEq` and `Eq`:
 
 ```
 #![feature(const_generics)]
 
-#[derive(PartialEq, Eq)]
+#[derive(PartialEq, Eq)] // We derive both traits here.
 struct A;
 
 struct B<const X: A>; // ok!