Changelog for 2.4

OpenPGP-Keychain/src/main/res/raw/help_changelog.html

@@ -23,6 +23,11 @@ Daniel Hammann, Daniel Haß, Greg Witczak, Miroojin Bakshi, Nikhil Peter Raj, Pa
 <li>and much more improvements and fixes…</li>
 </ul>
 
+<h2>2.3.1</h2>
+<ul>
+<li>hotfix for crash when upgrading from old versions</li>
+</ul>
+
 <h2>2.3</h2>
 <ul>
 <li>remove unnecessary export of public keys when exporting secret key (thanks to Ash Hughes)</li>