changelog: added documentation for the 2 new public functions

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/ChangeLog.d/7764.txt b/ChangeLog.d/7764.txt
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index 0000000..be332cd
--- /dev/null
+++ b/ChangeLog.d/7764.txt
@@ -0,0 +1,4 @@
+Features
+   * mbedtls_ecc_group_to_psa() and mbedtls_ecc_group_from_psa() helper
+     functions were added to convert from mbedtls_ecp_group_id to
+     psa_ecc_family_t and curve's bit size and viceversa, respectively.
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