Added release notes [ci skip]

docs/releasenotes/5.3.0.rst

@@ -39,6 +39,22 @@ and size, new method ``ImageOps.pad`` pads images to fill a requested aspect
 ratio and size, filling new space with a provided ``color`` and positioning the
 image within the new area through a ``centering`` argument.
 
+Image Size
+==========
+
+If you attempt to set the size of an image directly, e.g.
+``im.size = (100, 100)``, you will now receive an ``AttributeError``. This is
+not about removing existing functionality, but instead about raising an
+explicit error to prevent later consequences. The ``resize`` method is the
+correct way to change an image's size.
+
+The exceptions to this are:
+* The ICO and ICNS image formats, which use ``im.size = (100, 100)`` to select
+a subimage.
+* The TIFF image format, which now has a ``DeprecationWarning`` for this
+action, as direct image size setting was previously necessary to work around an
+issue with tile extents.
+
 Other Changes
 =============