Clarify layout of tuples when last field is unsized

Author: Darksonn

src/type-layout.md

@@ -121,6 +121,9 @@ r[layout.tuple.unit]
 The exception to this is the unit tuple (`()`), which is guaranteed as a
 zero-sized type to have a size of 0 and an alignment of 1.
 
+> [!NOTE]
+> It is not guaranteed that the last field of a tuple is stored at the end. For example, this means that `(i32, [u8; 10])` and `(i32; [u8])` might *not* have compatible layouts.
+
 r[layout.trait-object]
 ## Trait Object Layout