add changelog

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/ChangeLog.d/7765.txt b/ChangeLog.d/7765.txt
new file mode 100644
index 0000000..3dd6b5d
--- /dev/null
+++ b/ChangeLog.d/7765.txt
@@ -0,0 +1,3 @@
+Features
+   * Add functions mbedtls_ecdsa_raw_to_der() and mbedtls_ecdsa_der_to_raw() to
+     convert ECDSA signatures between raw and DER (ASN.1) formats.