docs: update changelog for v2.6.0-beta

changelogs/v2.6.0-beta.md

@@ -22,6 +22,11 @@ Thanks to all the people who have contributed to this release (including our [Cr
   - `Long select` (editor text action): Allows selecting long text efficiently without using the selection handle.
   - `Launch app`: Launches the already installed application.
 - New preferences:
+  - Preference to choose AndroidIDE's theme (requires restart if changed) :
+    - Blue wave - new default theme
+    - Sunny glow - the previous (yellowish) theme
+    - Material You
+  - Preference to choose language for AndroidIDE. Per-app language support has been added for Android 13+ devices.
   - Preference to enable/disable sticky scroll in the editor (disabled by default).
   - Preference to automatically launch application after build & install (disabled by default).
   - Preference to enable/disable line number pinning in editor (enabled by default).