Fix this comment

src/test/scala/leon/regression/verification/XLangVerificationSuite.scala

@@ -4,6 +4,8 @@ package leon.regression.verification
 
 import smtlib.interpreters.Z3Interpreter
 
+// If you add another regression test, make sure it contains exactly one object, whose name matches the file name.
+// This is because we compile all tests from each folder together.
 class XLangVerificationSuite extends VerificationSuite {
 
   val optionVariants: List[List[String]] = {