Updated Runtime Environments (markdown)

Runtime-Environments.md

@@ -42,6 +42,7 @@ The solutions of Go has to be located only in one package, the standard `main` e
 
 By default, we use a script that looks for a class with a `main` method and executes it for running Java programs. There has to be only one class containing `main` method, otherwise error will be observed. The executed script is named `javarun.java` and can be found in the [utils](https://github.com/ReCodEx/utils/blob/master/runners/java/javarun.java) repository. In tested solutions we use its byte-compiled counterpart `javarun.class`, so be aware of name collisions.
 
+Please note that the solution source codes cannot use subdirectories. I.e., the whole source code structure has to be flat. This is specially limiting for Java since it enforces all classes to dwell in the default package.
 
 ## Pascal