Backward compatibility: the key store with drivers

Promise that we will try to keep backward compatibility with basic driver
usage, but not with more experimental aspects.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h
index 65260bc..f9642e7 100644
--- a/include/mbedtls/mbedtls_config.h
+++ b/include/mbedtls/mbedtls_config.h
@@ -1184,8 +1184,9 @@
  *
  * Requires: MBEDTLS_PSA_CRYPTO_C
  *
- * \warning This interface is experimental and may change or be removed
- * without notice.
+ * \warning This interface is experimental. We intend to maintain backward
+ *          compatibility with application code that relies on drivers,
+ *          but the driver interfaces may change without notice.
  */
 //#define MBEDTLS_PSA_CRYPTO_DRIVERS