Add MBEDTLS_CHECK_RETURN description to config.h

Signed-off-by: Mateusz Starzyk <mateusz.starzyk@mobica.com>
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index e2f460c..b9e57eb 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -3695,6 +3695,18 @@
  */
 //#define MBEDTLS_PARAM_FAILED( cond )               assert( cond )
 
+/** \def MBEDTLS_CHECK_RETURN
+ *
+ * This macro appearing at the beginning of the declaration of a function
+ * indicates that its return value should be checked.
+ *
+ * Default implementation resides in platform_util.h.
+ * You can override default implementation by defining your own.
+ * Custom implementation can be empty, which will disable checking
+ * of functions' return values.
+ */
+//#define MBEDTLS_CHECK_RETURN
+
 /* PSA options */
 /**
  * Use HMAC_DRBG with the specified hash algorithm for HMAC_DRBG for the