Merge pull request #1500 from abarth/align_docs

Update the Align docs

packages/flutter/lib/src/rendering/shifted_box.dart

@@ -211,7 +211,7 @@ class RenderPadding extends RenderShiftedBox {
 ///
 /// For example, to align a box at the bottom right, you would pass this box a
 /// tight constraint that is bigger than the child's natural size,
-/// with the alignment set to (1.0, 1.0).
+/// with an alignment of [const FractionalOffset(1.0, 1.0)].
 ///
 /// By default, sizes to be as big as possible in both axes. If either axis is
 /// unconstrained, then in that direction it will be sized to fit the child's

packages/flutter/lib/src/widgets/basic.dart

@@ -359,7 +359,12 @@ class Padding extends OneChildRenderObjectWidget {
 ///
 /// For example, to align a box at the bottom right, you would pass this box a
 /// tight constraint that is bigger than the child's natural size,
-/// with horizontal and vertical set to 1.0.
+/// with an alignment of [const FractionalOffset(1.0, 1.0)].
+///
+/// By default, sizes to be as big as possible in both axes. If either axis is
+/// unconstrained, then in that direction it will be sized to fit the child's
+/// dimensions. Using widthFactor and heightFactor you can force this latter
+/// behaviour in all cases.
 class Align extends OneChildRenderObjectWidget {
   Align({
     Key key,