Add changelog for 260
This MR was automatically created from CI, https://gitlab.com/gitlab-org/gitter/gitter-android-app/-/jobs/137400984
We copied CURRENT_VERSION.txt
-> 260.txt
This MR was automatically created from CI, https://gitlab.com/gitlab-org/gitter/gitter-android-app/-/jobs/137400984
We copied CURRENT_VERSION.txt
-> 260.txt