Added changelog entry.

Signed-off-by: Ashley Duncan <ashley.duncan@evnex.com>
diff --git a/ChangeLog.d/mbedtls_ssl_read_undefined_behavior.txt b/ChangeLog.d/mbedtls_ssl_read_undefined_behavior.txt
new file mode 100644
index 0000000..392a91b
--- /dev/null
+++ b/ChangeLog.d/mbedtls_ssl_read_undefined_behavior.txt
@@ -0,0 +1,2 @@
+Bugfix
+   * Fixed undefined behavior in mbedtls_ssl_read if len argument is 0