Improve E0062 error explanation

Author: GuillaumeGomez

src/librustc_typeck/diagnostics.rs

@@ -640,8 +640,32 @@ variadic functions (except for its C-FFI).
 
 E0062: r##"
 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.
+enum variant, one of the fields was specified more than once. Erroneous code
+example:
+
+```
+struct Foo {
+    x: i32
+}
+
+fn main() {
+    let x = Foo { x: 0,
+                  x: 0, // error: field `x` specified more than once
+                };
+}
+```
+
+Each field should be specified exactly one time. Example:
+
+```
+struct Foo {
+    x: i32
+}
+
+fn main() {
+    let x = Foo { x: 0 }; // ok!
+}
+```
 "##,
 
 E0063: r##"