Add line break

Author: chansuke

compiler/rustc_error_codes/src/error_codes/E0779.md

@@ -5,7 +5,8 @@ Erroneous code example:
 ```compile_fail,E0779
 #![feature(isa_attribute)]
 
-#[instruction_set(intel::x64)] // error: `[instruction_set]` attribute argument should be valid
+#[instruction_set(intel::x64)] // error: `[instruction_set]` attribute argument
+                               //        should be valid
 pub fn something() {}
 fn main() {}
 ```