Fix the errors

Author: ubsan

src/doc/trpl/inline-assembly.md

@@ -107,6 +107,7 @@ operand. This is useful for very low level programming, where
 which register you use is important:
 
 ```
+# #![feature(asm)]
 # #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
 # unsafe fn read_byte_in(port: u16) -> u8 {
 let result: u8;
@@ -163,5 +164,5 @@ unsafe {
    asm!("mov eax, 2" : "={eax}"(result) : : : "intel")
 }
 println!("eax is currently {}", result);
-# } }
+# }
 ```