Update from transifex

OpenKeychain/src/main/res/raw-cs/help_changelog.md

@@ -1,5 +1,10 @@
 [//]: # (NOTE: Please put every sentence in its own line, Transifex puts every line in its own translation field!)
 
+## 4.9
+
+  * Curve25519 support
+  * Improved support for security tokens
+
 ## 4.8
 
   * Improved support for USB tokens: Gnuk, Nitrokey models, YubiKey 4 models