added an explanation for State class

src/detail/vst3/os/osutil.h

@@ -14,9 +14,17 @@
 
 namespace os
 {
-
+  
 class State
 {
+  // the State class ensures that a specific function pair (like init/terminate) is only called in pairs.
+  // the bool _state reflects if the _on lambda has already been called
+  // on destruction, it makes sure that the _off lambda is definitely called.
+  //
+  // the construct should only be applied to when no state machine can cover this properly
+  // or your own code depends on correct calling sequences of an external code base and should
+  // help to implement defensive programming.
+
  public:
   State(std::function<void()> on, std::function<void()> off) : _on(on), _off(off)
   {