docs: Add mention to the quickstart in the main README.md

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ENG-4088 Took 5 minutes

examples/quickstart/README.md

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+# QuickStart
+
+This quickstart guide enables you to:
+
+1. Create a Solution object
+2. Encode the solution to interact with the Ethereum blockchain
+
+## How to run
+
+```bash
+cargo run --release --example quickstart
+```