Clarify the unused lint clause in naked functions

This simply points out which warning is actually being disabled.

Author: npmccallum

text/2972-constrained-naked.md

@@ -32,7 +32,7 @@ A naked function is identified by the `#[naked]` attribute and:
 In exchange for the above constraints, the compiler commits to:
 1. produce a clear error if any of the above requirements are violated.
 1. produce a clear warning if any of the above suggestions are not heeded.
-1. disable the unused argument lint for the function.
+1. disable the unused argument lint for the function (implicit `#[allow(unused_variables)]`).
 1. never inline the function (implicit `#[inline(never)]`).
 1. emit no additional instructions to the function body before the `asm!()` statement.