Add ChangeLog

Signed-off-by: Ben Taylor <ben.taylor@linaro.org>
diff --git a/ChangeLog.d/remove_mbedtls_pk_type.txt b/ChangeLog.d/remove_mbedtls_pk_type.txt
new file mode 100644
index 0000000..0ad38e0
--- /dev/null
+++ b/ChangeLog.d/remove_mbedtls_pk_type.txt
@@ -0,0 +1,4 @@
+
+Removals
+   * Remove mbedtls_pk_type_t from the public interface and replace it with
+     mbedtls_pk_sigalg_t.