Update src/items/functions.md

Co-Authored-By: Mazdak Farrokhzad <[email protected]>

Author: nikomatsakis

src/items/functions.md

@@ -265,7 +265,7 @@ async unsafe fn unsafe_example(x: *const i32) -> i32 {
 }
 
 async fn safe_example() {
-    // Unsafe keyword required to invoke the function
+    // An `unsafe` block is required to invoke the function initially:
     // initially:
     let p = 22;
     let future = unsafe { unsafe_example(&p) };