Add ChangeLog entry for string-to-OID parsing

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/ChangeLog.d/oid-parse-from-numeric-string.txt b/ChangeLog.d/oid-parse-from-numeric-string.txt
new file mode 100644
index 0000000..459bedc
--- /dev/null
+++ b/ChangeLog.d/oid-parse-from-numeric-string.txt
@@ -0,0 +1,3 @@
+Features
+   * Add a function mbedtls_oid_from_numeric_string to parse an OID from a
+     string to a DER-encoded mbedtls_asn1_buf.