Add ChangeLog entry
diff --git a/ChangeLog b/ChangeLog
index 8f0e8c1..22d7dd4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS x.xx.x branch released xxxx-xx-xx
+
+Bugfix
+   * Fix private key DER output in the key_app_writer example. File contents
+     were shifted by one byte, creating an invalid ASN.1 tag. Fixed by
+     Christian Walther in #2239.
+
 = mbed TLS 2.14.0 branch released 2018-11-19
 
 Security