Add Changelog entry

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/ChangeLog.d/fix-gettimeofday-overflow.txt b/ChangeLog.d/fix-gettimeofday-overflow.txt
new file mode 100644
index 0000000..99a049d
--- /dev/null
+++ b/ChangeLog.d/fix-gettimeofday-overflow.txt
@@ -0,0 +1,4 @@
+Bugfix
+   * Fix possible integer overflow in mbedtls_timing_hardclock(), which
+     could cause a crash for certain platforms & compiler options.
+