Add instructions for running example app

Move useful information from CONTRIBUTING.md to the example-app/README.md

Author: andriy-shevtsov-moc

CONTRIBUTING.md

@@ -1,12 +1,74 @@
-## Created with Capacitor Create App
+### Running this example application
 
-This app was created using [`@capacitor/create-app`](https://github.com/ionic-team/create-capacitor-app),
-and comes with a very minimal shell for building an app.
+To run the provided example application, complete the following steps:
 
-### Running this example
+1. Clone the repository:
+ ```bash
+ git clone https://github.com/salemove/widgets_sdk_ionic.git
+ ```
+2. Navigate to the project directory:
+ ```bash
+ cd widgets_sdk_ionic
+ ```
+3. Install dependencies:
+ ```bash
+ npm install
+ ```
+4. Build the SDK:
+ ```bash
+ npm run build
+ ```
+5. Navigate to the example app directory:
+ ```bash
+ cd example-app
+ ```
+6. Create the environment file and add your Glia credentials:
+    - Create the file: `example-app/src/environments/environment.ts`.
+    - Refer to the [How to use environment variables?](#how-to-use-environment-variables) section for the instructions on how to add your Glia credentials.
+7. Install dependencies for the example app:
+ ```bash
+ npm install --legacy-peer-deps
+ ```
+8. Build the example app:
+ ```bash
+ npm run build
+ ```
+9. Sync with Capacitor:
+ ```bash
+ npx cap sync
+ ```
+10. Open the Android project (`widgets_sdk_ionic/example-app/android`) in Android Studio:
+    - Sync the project with Gradle.
+    - Run the Android app.
+11. Open the iOS project (`widgets_sdk_ionic/example-app/ios`) in Xcode:
+    - Run the iOS app.
 
-To run the provided example, you can use `npm start` command.
+### How to use environment variables?
 
-```bash
-npm start
+- Create an `environments` folder inside the `src` folder, and then create the `environment.ts` file inside it: `example-app/src/environments/environment.ts`.
+- Add all environment variables to the `environment.ts` (replace the example values with your data):
+
+```typescript
+export const environment = {
+  IONIC_API_KEY: 'site-api-key',
+  IONIC_API_SECRET: 'site-api-secret',
+  IONIC_SITE_ID: 'site-identifier',
+  IONIC_REGION: 'us',
+  IONIC_COMPANY_NAME: 'IonicCompany',
+};
 ```
+
+After environment variables are defined:
+
+1. Open the `example-app` folder.
+2. Run `npm run build`.
+3. Run `npx cap sync`.
+
+ℹ️ Since Ionic is built on top of Angular, the example app project uses Angular’s built-in mechanism for managing environment variables. You can refer to the official Angular documentation [here](https://v17.angular.io/guide/build).
+
+### Troubleshooting
+
+To be sure that environment variables have been applied correctly, open the `public` folder and find the `index-#{some_hash}.js` file. If the variables were applied correctly, you should see something like this in Android Studio and Xcode, respectively:
+![image](/image/406754853-aff92ca8-14e1-4ba3-a89c-c20569880d55.png)
+![image](/image/406755039-3cf54cb1-fb3c-4eab-a494-3c92cb13cbfa.png)
+