Document the demo

docs/Demo.md

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+# Demo
+
+## Getting Started
+
+See "Running the demo" in `README.md`.
+
+## Behind the scenes
+
+The demo webapp is made with a lightweight node.js webserver called `lite-server`. Once the `demo`
+command is called, a new tab should open in your default browser to a splash screen called "Signal
+Token Protocol Demo".
+
+On load, the webapp will attempt to connect to a local Ethereum net at `localhost:9545` and deploy a
+`SignalTokenProtocol` contract to it. It will also grant the first address in your local net
+500000 SIG tokens.
+
+Enter an "Amount per Referral". On submit, a campaign is created and stored in the
+`SignalTokenProtocol` contract. The contract then queries the `TokenStub` contract and retrieves
+ balances for the relevant accounts.
+
+Click the "spectiv" banner. When you do, the campaign you created in the previous step will be
+executed by the executor (in this case, the web application) and you should see the address
+balances update as the advertiser sends the agreed upon sum of SIG tokens to the publisher.