Add Upgrade to V6 readme file, other minor fixes

typos in config file
deprecate read env file function, use class instead
add read/write menu_flag in Class\Backend, further updates in later
versions

www/configs/read_env_file.php

@@ -25,9 +25,15 @@ declare(strict_types=1);
  *                          1 for file loadable, but no data inside
  *                          2 for file not readable
  *                          3 for file not found
+ * @deprecated V6 Use \CoreLibs\Get\ReadEnvFile::readEnvFile()
  */
 function readEnvFile(string $path = __DIR__, string $env_file = '.env'): int
 {
+	trigger_error(
+		'Method readEnvFile() is deprecated, use '
+			. '\CoreLibs\Get\ReadEnvFile::readEnvFile()',
+		E_USER_DEPRECATED
+	);
 	// default -1;
 	$status = -1;
 	$env_file_target = $path . DIRECTORY_SEPARATOR . $env_file;