Addition of the migration guide and change log files

Signed-off-by: TRodziewicz <tomasz.rodziewicz@mobica.com>
diff --git a/ChangeLog.d/issue4083.txt b/ChangeLog.d/issue4083.txt
new file mode 100644
index 0000000..f3f7e31
--- /dev/null
+++ b/ChangeLog.d/issue4083.txt
@@ -0,0 +1,5 @@
+Changes
+    * Remove the following functions: mbedtls_timing_self_test() and
+      mbedtls_hardclock_poll(). Move the following functions to the benchmark.c
+      file and make them static: mbedtls_timing_hardclock() and
+      mbedtls_set_alarm(). Fixes #4083.