Add changelog for 0.31.0

CHANGELOG.md

+## 0.31.0 (2024-10-24)
+
+### Changed (1 change)
+
+- [Improve documentation around module release](https://gitlab.com/components/opentofu/-/commit/1deda55c7f4a12b69b439af0f6d2eec4e9b97783) ([merge request](https://gitlab.com/components/opentofu/-/merge_requests/139))
+
 ## 0.30.0 (2024-10-07)
 
 No changes.