Clean up E0062 long explanation

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0062.md

@@ -1,6 +1,6 @@
-This error indicates that during an attempt to build a struct or struct-like
-enum variant, one of the fields was specified more than once. Erroneous code
-example:
+A struct's or struct-like enum variant's field was specified more than once.
+
+Erroneous code example:
 
 ```compile_fail,E0062
 struct Foo {
@@ -15,7 +15,9 @@ fn main() {
 }
 ```
 
-Each field should be specified exactly one time. Example:
+This error indicates that during an attempt to build a struct or struct-like
+enum variant, one of the fields was specified more than once. Each field should
+be specified exactly one time. Example:
 
 ```
 struct Foo {