Clean up E0080 long explanation

src/librustc_error_codes/error_codes/E0080.md

@@ -1,14 +1,18 @@
-This error indicates that the compiler was unable to sensibly evaluate a
-constant expression that had to be evaluated. Attempting to divide by 0
-or causing integer overflow are two ways to induce this error. For example:
+A constant value failed to get evaluated.
+
+Erroneous code example:
 
 ```compile_fail,E0080
 enum Enum {
     X = (1 << 500),
-    Y = (1 / 0)
+    Y = (1 / 0),
 }
 ```
 
+This error indicates that the compiler was unable to sensibly evaluate a
+constant expression that had to be evaluated. Attempting to divide by 0
+or causing an integer overflow are two ways to induce this error.
+
 Ensure that the expressions given can be evaluated as the desired integer type.
 See the FFI section of the Reference for more information about using a custom
 integer type: