readme update, screenshot added

Author: szymor

README.md

@@ -1,9 +1,10 @@
-=== Tiny OPK Viewer ===
+# Tiny OPK Viewer
 
 A simple tool for viewing OpenDingux and RetroFW packages. It supports opening OPKs from both CLI and GUI.
 
-=== to do list ===
+![Screenshot](screenshot1.png)
+
+## To Do List
 - support for multiple open files (multitab view, cmdline)
 - image viewer navigation in case of multiple images in the root directory
-- windows port
 - maybe C++ port