Add ChangeLog entry
diff --git a/ChangeLog b/ChangeLog
index 98776ec..e431d8d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -6,6 +6,8 @@
    * Fix memory leak in ssl_set_hostname() when called multiple times.
      Found by projectgus and jethrogb, #836.
    * Fix usage help in ssl_server2 example. Found and fixed by Bei Lin.
+   * Fix Visual Studio implicit cast compilation warnings in the net.c and
+     x509.c modules and some sample applications.
 
 = mbed TLS 1.3.21 branch released 2017-08-10