Improve E0601 explanation

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0601.md

@@ -1,5 +1,6 @@
-No `main` function was found in a binary crate. To fix this error, add a
-`main` function. For example:
+No `main` function was found in a binary crate.
+
+To fix this error, add a `main` function:
 
 ```
 fn main() {