added ReadMe file for expo quickstart sample app (#1367)

### Pre-launch Checklist

- [x] The [Documentation] is updated accordingly, or this PR doesn't
require it.
- [x] I have updated the `ExampleAppChangelog.txt` file with relevant
changes.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I added new tests to check the change I am making, or this PR is
test-exempt.
- [x] All existing and new tests are passing.

<!-- Links -->

[Documentation]: https://www.100ms.live/docs

sample-apps/rnhms-expo-demo/README.md

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+# Expo & Prebuilt Sample App
+
+This Expo app uses `@100mslive/react-native-room-kit` package for adding video calling feature.
+
+To add video calling feature into your own Expo app, You can refer [Expo & Prebuilt Quickstart guide](https://www.100ms.live/docs/react-native/v2/quickstart/expo-prebuilt)
+
+You can also build this app locally on your machine -
+
+1. Fork and clone the repo
+2. Change your current working directory to `..../sample-apps/rnhms-expo-demo` dir.
+3. Install `node_modules` by running `npx expo install`.
+4. You Need to have `Node.js >= 18`, You can check your node version by running `node -v`. You can use [nvm](https://github.com/nvm-sh/nvm) or upgarde your node version.
+5. Recreate `android` and `ios` folders by running `npx expo prebuild`.
+6. Now you should be able to run apps by running `npm run android` or `npm run ios`.
+
+## Android Setup
+
+Android app is targeting `Android SDK 34`. Therefore, You will need `JDK 17` to build the Android app.
+
+You can check your JDK version by running `java --version` in terminal.