CHANGELOG: Add last two production releases, fix dates, add link

* Added 3.26.0
* Added 3.25.0
* Fixed year on 3.24.1
* Added milestone link on existing 3.24.1 entry to match others

Also related to this PR:
- fixed the dates on the 3.24.x releases in GH (https://github.com/nextcloud/android/releases)
- added a missing milestone link

Signed-off-by: Josh Richards <josh.t.richards@gmail.com>

CHANGELOG.md

@@ -1,9 +1,30 @@
-## 3.24.1 (February 21, 2022)
+## 3.26.0 (September 16, 2023)
+
+- image editing
+- image details, with map
+- show other Nextcloud apps
+
+Minimum: NC 16 Server, Android 6.0 Marshmallow
+
+For a full list, please see https://github.com/nextcloud/android/milestone/84
+
+## 3.25.0 (June 13, 2023)
+
+- show Groupfolder
+- Tag in file listing
+
+Minimum: NC 16 Server, Android 6.0 Marshmallow
+
+For a full list, please see https://github.com/nextcloud/android/milestone/81
+
+## 3.24.1 (February 21, 2023)
 
 - Fix crash in previous version when connecting to old server versions
 
 Minimum: NC 16 Server, Android 6.0 Marshmallow
 
+For a full list, please see https://github.com/nextcloud/android/milestone/80
+
 ## 3.24.0 (February 13, 2023)
 
 - Several performance optimizations by @starypatyk