docs: update changelog.

Author: whitequark

docs/changes.rst

@@ -9,6 +9,7 @@ Documentation for past releases
 
 Documentation for past releases of the Amaranth language and toolchain is available online:
 
+* `Amaranth 0.5.8 <https://amaranth-lang.org/docs/amaranth/v0.5.8/>`_
 * `Amaranth 0.5.7 <https://amaranth-lang.org/docs/amaranth/v0.5.7/>`_
 * `Amaranth 0.5.6 <https://amaranth-lang.org/docs/amaranth/v0.5.6/>`_
 * `Amaranth 0.5.5 <https://amaranth-lang.org/docs/amaranth/v0.5.5/>`_
@@ -26,6 +27,15 @@ Documentation for past releases of the Amaranth language and toolchain is availa
 * `Amaranth 0.3 <https://amaranth-lang.org/docs/amaranth/v0.3/>`_
 
 
+Version 0.5.9
+=============
+
+Platform integration changes
+----------------------------
+
+* Fixed: ECP5 DDR buffer output enable latency to match output latency.
+
+
 Version 0.5.8
 =============