Readme: mention ignoreUnknownFunctions (#126)

Author: janedbal

README.md

@@ -148,13 +148,14 @@ return $config
     // for multiple, use ignoreErrorsOnPackagesAndPaths() or ignoreErrorsOnPackageAndPaths()
     ->ignoreErrorsOnPackageAndPath('symfony/console', __DIR__ . '/src/OptionalCommand.php', [ErrorType::SHADOW_DEPENDENCY])
 
-    // allow using classes not present in composer's autoloader
+    // allow using non-autoloadable classes
     // e.g. a library may conditionally support some feature only when Memcached is available
     ->ignoreUnknownClasses(['Memcached'])
+    ->ignoreUnknownClassesRegex('~^DDTrace~')
 
-    // allow using classes not present in composer's autoloader by regex
-    // e.g. when you want to ignore whole namespace of classes
-    ->ignoreUnknownClassesRegex('~^PHPStan\\.*?~')
+    // allow using functions not defined during runtime
+    ->ignoreUnknownFunctions(['opcache_invalidate'])
+    ->ignoreUnknownFunctionsRegex('~^opcache_~')
 
     // force certain classes to be treated as used
     // handy when dealing with dependencies in non-php files (e.g. DIC config), see example below