Add step-by-step instructions to README.md

I was working on the getting started docs in FireFly, and I wanted to defer all the samples related docs to point at the README. md in this repo.

However, unless you're a Node.js developer I don't think currently there's quite enough info in this repo to get people started.

Here's what was in the docs on the FireFly side, which I'm pulling out.
I think even this is a little bit less than the step by step someone might need.

... raising a separate issue for a discussion on getting a Docker built samples gallery

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This repository contains two straightforward, turnkey samples. A simple CLI-based flow, and a more robust flow with a React frontend, with the option for customized recipients and messaging strings.

* [FireFly Samples Repo](https://github.com/hyperledger-labs/firefly-samples)
- clone this ^^
* [Node.js](https://nodejs.org/en/download/) - latest version recommended (v14.17.0)
- `node -v` to check your current version
* Install the node dependencies in **each** folder: (`/firefly-samples/private-data-transfer-cli` & `/firefly-samples/private-data-transfer-ui`) with `npm install`.
* The following command: `npm run start` will kick either program. Run the command separately from the root of each project.
- The "Private-Data-Transfer-Cli" will self execute with a message broadcast and acknowledgement of message receipt.
- The "Private-Data-Transfer-UI" will serve locally on port 3000. You can toggle amongst your FireFly memberships to see different message/transaction details - timestamp, sender and inputs.