Improve E0057 long error explanation

src/librustc_error_codes/error_codes/E0057.md

@@ -1,8 +1,6 @@
-When invoking closures or other implementations of the function traits `Fn`,
-`FnMut` or `FnOnce` using call notation, the number of parameters passed to the
-function must match its definition.
+An invalid number of arguments was given when calling a closure.
 
-An example using a closure:
+Erroneous code example:
 
 ```compile_fail,E0057
 let f = |x| x * 3;
@@ -11,6 +9,10 @@ let b = f(4);       // this works!
 let c = f(2, 3);    // invalid, too many parameters
 ```
 
+When invoking closures or other implementations of the function traits `Fn`,
+`FnMut` or `FnOnce` using call notation, the number of parameters passed to the
+function must match its definition.
+
 A generic function must be treated similarly:
 
 ```