Meta: Update changelog

Author: Joseph-Edwards

docs/source/changelog-v1.rst

@@ -8,7 +8,18 @@
 Changelog - version 1
 =====================
 
-v1.0.0 (released ??/??/202?)
+v1.0.0 (released 12/08/2025)
 -----------------------------
 
-TODO
+This is a major release that significantly expands the API of
+``libsemigroups_pybind11`` to expose much of the functionality implemented in
+version 3 of libsemigroups_. The extent of the changes made in this release
+means that it is likely that any code written with earlier versions of
+``libsemigroups_pybin11`` will no longer work.
+
+The structure of ``libsemigroups_pybind11`` is very tightly linked to the the
+structure of libsemigroups_. Therefore, some of the differences between
+v0.10.1 and v1.0.0 of ``libsemigroups_pyind11`` will be related to the
+differences between v2 and v3 of libsemigroups_, such as changes to class names
+and interfaces. These changes can be found in the
+`libsemigroups changelog <https://libsemigroups.github.io/libsemigroups/md_changelog-v3.html>`_.