Improve wording

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0752.md

@@ -8,9 +8,9 @@ async fn main() -> Result<i32, ()> { // error!
 }
 ```
 
-`fn main()` or the specified start function is not allowed to be `async`. You
-might be seeing this error because your async runtime library is not set up
-correctly. To fix it, don't declare the entry point as `async`:
+`fn main()` or the specified start function is not allowed to be `async`. Not
+having a correct async runtime library setup may cause this error. To fix it,
+declare the entry point without `async`:
 
 ```
 fn main() -> Result<i32, ()> { // ok!