Improve Layout::extend docs

Author: CAD97

src/libcore/alloc/layout.rs

@@ -258,9 +258,10 @@ impl Layout {
 
     /// Creates a layout describing the record for `self` followed by
     /// `next`, including any necessary padding to ensure that `next`
-    /// will be properly aligned, but *no trailing padding*. In order
-    /// to match C representation layout `repr(C)`, you should call
-    /// `pad_to_align` after extending the layout with all fields.
+    /// will be properly aligned, but *no trailing padding*.
+    ///
+    /// In order to match C representation layout `repr(C)`, you should
+    /// call `pad_to_align` after extending the layout with all fields.
     /// (There is no way to match the default Rust representation
     /// layout `repr(Rust)`, as it is unspecified.)
     ///