add plantUML for th_searchArena

conception/th_searchArena.txt

@@ -0,0 +1,25 @@
+@startuml
+skinparam monochrome true
+start
+while ()
+	:searchArena?;
+	:shouldSendImage = false;
+	:Img img = camera.Grab();
+	:arena = img.SearchArena();
+	if (arena) then (nullptr)
+		:msg = new Message(MESSAGE_ANSWER_NACK);
+		:messageToMonitor!msg;	
+	else () 
+		:img = img.DrawArena(arena);
+		:msg = new MessageImg(MESSAGE_CAM_IMAGE, img);
+		:messageToMon!msg;
+		:validateArena?arenaOk;
+		if (arenaOk) then (false)
+			:arena = nullptr;
+		else (true)
+		endif;
+	endif;
+	:shouldSendImg = true;
+end while;
+stop
+@enduml