chore: update example documentation

Author: Alex Thomas

example/README.md

@@ -0,0 +1,10 @@
+# Example
+Before executing this example, you must create a `.env` file within this directory with the following contents:
+
+```
+URL=https://ropsten.infura.io/v3/<your-api-token>
+```
+
+You can create an API key for the Ropsten test network [here](https://ropsten.etherscan.io/apis).
+
+Once this is done, go ahead and execute `yarn android` or `yarn ios` to start experimenting.