Fix comment

xtensa-lx/src/interrupt.rs

@@ -152,7 +152,10 @@ pub fn get_level() -> u32 {
 
 /// Execute closure `f` in an interrupt-free context.
 ///
-/// This as also known as a "critical section".
+/// This method does not synchronise multiple cores, so it is not suitable for
+/// using as a critical section. See the `critical-section` crate for a
+/// cross-platform way to enter a critical section which provides a
+/// `CriticalSection` token.
 #[inline]
 pub fn free<F, R>(f: F) -> R
 where