Add example code and round ruler

README.md

@@ -1,2 +1,66 @@
 # display-ruler
-Display test image
+Display test image useful for checking size, alignment and color order.
+
+## Small rectangular displays
+```python
+import displayio
+
+# Initialize the display in the display variable
+ruler = displayio.OnDiskBitmap("/display-ruler.bmp")
+
+t = displayio.TileGrid(ruler, pixel_shader=ruler.pixel_shader)
+
+g = displayio.Group()
+g.append(t)
+
+display.show(g)
+
+display.refresh()
+
+while True:
+    pass
+```
+
+## Large rectangular displays
+```python
+import displayio
+
+# Initialize the display in the display variable
+ruler = displayio.OnDiskBitmap("/display-ruler-720p.bmp")
+
+t = displayio.TileGrid(ruler, pixel_shader=ruler.pixel_shader)
+
+g = displayio.Group()
+g.append(t)
+
+display.show(g)
+
+display.refresh()
+
+while True:
+    pass
+```
+
+## Round displays
+
+```python
+import displayio
+
+# Initialize the display in the display variable
+ruler = displayio.OnDiskBitmap("/round-display-ruler-720p.bmp")
+
+t = displayio.TileGrid(ruler, pixel_shader=ruler.pixel_shader)
+# Center the image
+t.x -= (ruler.width - display.width) // 2
+t.y -= (ruler.height - display.height) // 2
+
+g = displayio.Group()
+g.append(t)
+
+display.show(g)
+
+display.refresh()
+
+while True:
+    pass
+```