Reference get_version_number from the conf_xxx_version documentation

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index a2b4cdd..b964c4e 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -3745,6 +3745,10 @@
  *
  * \note           With DTLS, use MBEDTLS_SSL_MINOR_VERSION_3 for DTLS 1.2
  *
+ * \note           After the handhsake, you can call
+ *                 mbedtls_ssl_get_version_number() to see what version was
+ *                 negotiated.
+ *
  * \param conf     SSL configuration
  * \param major    Major version number (only MBEDTLS_SSL_MAJOR_VERSION_3 supported)
  * \param minor    Minor version number (only MBEDTLS_SSL_MINOR_VERSION_3 supported)
@@ -3760,6 +3764,10 @@
  *
  * \note           With DTLS, use MBEDTLS_SSL_MINOR_VERSION_3 for DTLS 1.2
  *
+ * \note           After the handhsake, you can call
+ *                 mbedtls_ssl_get_version_number() to see what version was
+ *                 negotiated.
+ *
  * \param conf     SSL configuration
  * \param major    Major version number (only MBEDTLS_SSL_MAJOR_VERSION_3 supported)
  * \param minor    Minor version number (only MBEDTLS_SSL_MINOR_VERSION_3 supported)