improve example

fix bug that R wasn't shown and add antother example for showing a picture

main.py

@@ -10,7 +10,12 @@ shield = WEMOSMatrixLEDShield()
 
 while True:
     scroll("Hallo Welt!",5,30)
+    shield.blit(get_picture("diamond"))
+    shield.update()
+    sleep(1)
     shield.blit(letter("R"), (0, 0))
+    shield.update()
+    sleep(0.5)
     heart = get_picture("heart")
     for i in range(8):
         shield.blit(heart, (0, 0))