Add changelog for 3.20.2

Signed-off-by: tobiasKaminsky <tobias@kaminsky.me>

CHANGELOG.md

@@ -1,3 +1,11 @@
+## 3.20.2 (June 9th, 2022)
+
+- Several minor bugfixes
+
+Minimum: NC 16 Server, Android 6.0 Marshmallow
+
+For a full list, please see https://github.com/nextcloud/android/milestone/68
+
 ## 3.20.1 (May 6th, 2022)
 
 - Several minor bugfixes