Update src/llff.rs

Co-authored-by: Zeeshan Ali Khan <[email protected]>

Author: JalonWong

src/llff.rs

@@ -41,7 +41,10 @@ impl Heap {
     ///
     /// # Safety
     ///
-    /// Please ensure that `start_addr`` points to valid memory and that `size`` is correct.
+    /// This function is safe if the following invariants hold:
+    ///
+    /// * `start_addr`` points to valid memory.
+    /// *  `size`` is correct.
     ///
     /// # Panics
     ///