Clean up E0745

src/librustc_error_codes/error_codes/E0745.md

@@ -1,20 +1,23 @@
-Cannot take address of temporary value.
+The address of temporary value was taken.
 
 Erroneous code example:
 
 ```compile_fail,E0745
 # #![feature(raw_ref_op)]
 fn temp_address() {
-    let ptr = &raw const 2;   // ERROR
+    let ptr = &raw const 2; // error!
 }
 ```
 
-To avoid the error, first bind the temporary to a named local variable.
+In this example, `2` is destroyed right after the assignment, which means that
+`ptr` now points to an unavailable location.
+
+To avoid this error, first bind the temporary to a named local variable:
 
 ```
 # #![feature(raw_ref_op)]
 fn temp_address() {
     let val = 2;
-    let ptr = &raw const val;
+    let ptr = &raw const val; // ok!
 }
 ```