Fix #12993: Replace known-bugs text with markdown version.

This allows a little bit better formatting/display in game.

(No attempt to check if these are still valid known-bugs...)

src/os/windows/win32.cpp

@@ -131,7 +131,7 @@ void CreateConsole()
 		_close(fd);
 		CloseHandle(hand);
 
-		ShowInfo("Unable to open an output handle to the console. Check known-bugs.txt for details.");
+		ShowInfo("Unable to open an output handle to the console. Check known-bugs.md for details.");
 		return;
 	}