Add Changelog entry

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/ChangeLog.d/fix-printf-specifiers.txt b/ChangeLog.d/fix-printf-specifiers.txt
new file mode 100644
index 0000000..72d08c0
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+++ b/ChangeLog.d/fix-printf-specifiers.txt
@@ -0,0 +1,10 @@
+Bugfix
+   * Add printf function attributes to mbedtls_debug_print_msg because we were
+     not actually getting any printf format specifier warnings prior to this.
+     Also add extra printf compiler warning flags to builds.
+Requirement Changes
+   * Use %zu for print of type size_t in new work, however please do not use
+     them in backports, and preferably not in code that needs to be
+     backported.
+
+