add changelog

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/ChangeLog.d/8710.txt b/ChangeLog.d/8710.txt
new file mode 100644
index 0000000..8ff23c5
--- /dev/null
+++ b/ChangeLog.d/8710.txt
@@ -0,0 +1,3 @@
+Features
+   * PK provides support for opaque keys as soon as MBEDTLS_CRYPTO_CLIENT is
+     enabled, regardless of the status of MBEDTLS_USE_PSA_CRYPTO.