[commands] Update Command documentation (NFC) (#3881)

Add reference to which VendorDep the class is included in.
Add missing OldCommands C++ Documentation (copied from Java).

wpilibNewCommands/src/main/native/include/frc2/command/WaitUntilCommand.h

@@ -15,6 +15,8 @@ namespace frc2 {
 /**
  * A command that does nothing but ends after a specified match time or
  * condition.  Useful for CommandGroups.
+ *
+ * This class is provided by the NewCommands VendorDep
  */
 class WaitUntilCommand : public CommandHelper<CommandBase, WaitUntilCommand> {
  public: