New page for 'create big image'

docs/reference/images/create-big-image.md

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+# Create Big Image
+
+Make a big [image](/reference/images/image) (picture) for the micro:bit
+[LED screen](/device/screen). The big image made of two squares.
+Each of the squares is five LEDs on a side, like a regular image.
+
+```blocks
+images.createBigImage(`
+    . . # . .   . . # . .
+    . # # # .   . . # . .
+    # . # . #   # . # . #
+    . . # . .   . # # # .
+    . . # . .   . . # . .
+    `);
+```
+
+### Example: Flip-flopping arrow
+
+This program makes a big image with a picture of an arrow pointing up,
+and an arrow pointing down.  If you press button `A`, the program will
+show the arrow pointing up, which starts `0` LEDs from the left in the
+big image.  If you press button `B`, the program will show the arrow
+pointing down, which starts `5` LEDs from the left.
+
+```blocks
+let arrows = images.createBigImage(`
+    . . # . .   . . # . .
+    . # # # .   . . # . .
+    # . # . #   # . # . #
+    . . # . .   . # # # .
+    . . # . .   . . # . .
+    `);
+input.onButtonPressed(Button.A, () => {
+    arrows.showImage(0);
+});
+input.onButtonPressed(Button.B, () => {
+    arrows.showImage(5);
+});
+```
+
+### See also
+
+[Getting Started](/reference/getting-started), [image](/reference/images/image),
+[create image](/reference/images/create-image),
+[show image](/reference/image/show-image),
+[scroll image](/reference/image/scroll-image), [show animation](/reference/basic/show-animation)