docs/changes: add 0.5.1 changes.

Author: wanda-phi

docs/changes.rst

@@ -18,6 +18,20 @@ Documentation for past releases of the Amaranth language and toolchain is availa
 * `Amaranth 0.3 <https://amaranth-lang.org/docs/amaranth/v0.3/>`_
 
 
+Version 0.5.1
+=============
+
+
+Standard library changes
+------------------------
+
+.. currentmodule:: amaranth.lib
+
+* Added: views of :class:`amaranth.lib.data.ArrayLayout` can be indexed with negative integers or slices.
+* Added: :py:`len()` works on views of :class:`amaranth.lib.data.ArrayLayout`.
+* Added: views of :class:`amaranth.lib.data.ArrayLayout` are iterable.
+
+
 Version 0.5
 ===========