rename gallery demo markdown and put in a number of commands

README-gallery-demo.md

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+## Gallery Pixel Demo
+
+In this Gallery Demo, the goal is to be able to create designs in a
+pixel canvas. You start with access to the gallery and a handful of
+methods that allow you to obtain pixels, color them, and buy or sell
+pixels. 
+
+To access the gallery, type `home.gallery` in the REPL. `home.gallery` is a
+Presence. In the SwingSet environment, Presences are remote references to objects on
+other vats. To invoke them, use the `E` wrapper. For example, the
+first thing you might want to do is tap the gallery faucet to get a
+pixel for free: 
+
+```js
+E(home.gallery).tapFaucet()
+```
+
+This returns a presence for the pixel that you receive from the
+faucet and saves it under `history[0]`.
+
+To color the pixel, we need to split the pixel into "transfer" and
+"use" rights. The right to use the pixel means that you can color it,
+and we'll be using it to color. 
+
+The following commands show a pixel being obtained from the faucet,
+being transformed into transfer and use rights, coloring the pixel by
+using the 'use' right, and selling a pixel to the gallery through a
+escrow smart contract.  
+
+```
+E(home.gallery).tapFaucet()
+E(home.gallery).transformToTransferAndUse(history[0])
+history[1].useRightPayment
+E(home.gallery).changeColor(history[2], '#FF69B4')
+E(home.gallery).tapFaucet()
+E(history[4]).getBalance()
+E(home.gallery).pricePixelAmount(history[5])
+E(home.gallery).sellToGallery(history[5])
+history[7].inviteP
+history[7].host
+E(history[9]).redeem(history[8])
+E(history[10]).offer(history[4])
+E(home.gallery).getIssuers()
+history[12].pixelIssuer
+history[12].dustIssuer
+E(history[13]).makeEmptyPurse()
+E(history[14]).makeEmptyPurse()
+E(home.gallery).collectFromGallery(history[10], history[16],
+history[15], 'my escrow')
+```