Improve ChangeLog entry

Signed-off-by: Ben Taylor <ben.taylor@linaro.org>
diff --git a/ChangeLog.d/replace_time_t.txt b/ChangeLog.d/replace_time_t.txt
index 53b63cf..ec0282a 100644
--- a/ChangeLog.d/replace_time_t.txt
+++ b/ChangeLog.d/replace_time_t.txt
@@ -1,3 +1,4 @@
 Bugfix
-   * Replace occurances of time_t with
-     mbedtls_time_t.
+   * Fix a build error or incorrect TLS session
+     lifetime on platforms where mbedtls_time_t
+     is not time_t. Fixes #10236.