Add changelog entry for ARM assembly fix

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index 37373a2..e1110a1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -79,6 +79,9 @@
      This previously limited the maximum size of DER encoded certificates
      in mbedtls_x509write_crt_der() to 2Kb. Reported by soccerGB in #2631.
    * Fix partial zeroing in x509_get_other_name. Found and fixed by ekse, #2716.
+   * Fix the build on ARMv5TE in ARM mode to not use assembly instructions
+     that are only available in Thumb mode. Fix contributed by Aurelien Jarno
+     in #2169.
 
 API Changes
    * Extend the MBEDTLS_SSL_EXPORT_KEYS to export the handshake randbytes,