Improve documentation of mbedtls_ssl_write()

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index aaf34fc..c3db587 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -54,6 +54,8 @@
      Wilson #481
    * Improve the documentation of mbedtls_net_accept(). Contributed by Ivan
      Krylov.
+   * Improve the documentation of mbedtls_ssl_write(). Suggested by
+     Paul Sokolovsky in #1356.
 
 = mbed TLS 2.8.0 branch released 2018-03-16