Add comprehensive README documentation

Author: ondrajodas

README.md

@@ -1,7 +1,183 @@
-# Keboola Google API Client
+# Keboola Google Client Bundle
 
-Basic client for Google APIs  
+Keboola Google API Client with OAuth 2.0 and Service Account authentication support.
+
+## Installation
+
+```bash
+composer require keboola/google-client-bundle
+```
+
+## Usage
+
+This library supports two types of authentication:
+
+1. **OAuth 2.0** - for applications that need access to user data
+2. **Service Account** - for server-to-server communication without user intervention
+
+### OAuth 2.0 Authentication
+
+#### Classic approach
+
+```php
+use Keboola\Google\ClientBundle\Google\RestApi;
+
+$api = new RestApi($logger); // Optional logger parameter
+$api->setAppCredentials($clientId, $clientSecret);
+$api->setCredentials($accessToken, $refreshToken);
+
+// Get authorization URL
+$authUrl = $api->getAuthorizationUrl(
+    'http://localhost/callback',
+    'https://www.googleapis.com/auth/drive.readonly',
+    'force',
+    'offline'
+);
+
+// Authorize using code
+$tokens = $api->authorize($code, 'http://localhost/callback');
+
+// API calls
+$response = $api->request('/drive/v2/files');
+```
+
+#### New factory approach
+
+```php
+use Keboola\Google\ClientBundle\Google\RestApi;
+
+$api = RestApi::createWithOAuth(
+    $clientId,
+    $clientSecret,
+    $accessToken,
+    $refreshToken
+);
+
+// Usage same as above
+$response = $api->request('/drive/v2/files');
+```
+
+### Service Account Authentication
+
+```php
+use Keboola\Google\ClientBundle\Google\RestApi;
+
+// Service account JSON configuration (from Google Cloud Console)
+$serviceAccountConfig = [
+    'type' => 'service_account',
+    'project_id' => 'your-project-id',
+    'private_key_id' => 'key-id',
+    'private_key' => '-----BEGIN PRIVATE KEY-----\n...\n-----END PRIVATE KEY-----\n',
+    'client_email' => 'your-service-account@your-project.iam.gserviceaccount.com',
+    'client_id' => '123456789',
+    'auth_uri' => 'https://accounts.google.com/o/oauth2/auth',
+    'token_uri' => 'https://oauth2.googleapis.com/token',
+    'auth_provider_x509_cert_url' => 'https://www.googleapis.com/oauth2/v1/certs',
+    'client_x509_cert_url' => 'https://www.googleapis.com/robot/v1/metadata/x509/your-service-account%40your-project.iam.gserviceaccount.com'
+];
+
+// Scope definitions
+$scopes = [
+    'https://www.googleapis.com/auth/cloud-platform',
+    'https://www.googleapis.com/auth/drive.readonly'
+];
+
+// Create API client
+$api = RestApi::createWithServiceAccount(
+    $serviceAccountConfig,
+    $scopes
+);
+
+// API calls
+$response = $api->request('/drive/v2/files');
+```
+
+#### Loading Service Account from JSON file
+
+```php
+use Keboola\Google\ClientBundle\Google\RestApi;
+
+// Load from JSON file
+$serviceAccountConfig = json_decode(
+    file_get_contents('/path/to/service-account-key.json'),
+    true
+);
+
+$scopes = ['https://www.googleapis.com/auth/cloud-platform'];
+
+$api = RestApi::createWithServiceAccount($serviceAccountConfig, $scopes);
+$response = $api->request('/your-api-endpoint');
+```
+
+## Differences between OAuth and Service Account
+
+| Property | OAuth 2.0 | Service Account |
+|----------|-----------|-----------------|
+| Authentication type | User-based | Server-to-server |
+| Refresh token | ✅ Yes | ❌ No (not needed) |
+| Authorization | Requires user consent | Automatic |
+| Usage | Access to user data | Access to application data |
+| Token expiration | Based on refresh token | Automatic renewal |
+
+## Advanced Usage
+
+### Retry and Backoff
+
+```php
+$api->setBackoffsCount(10); // Number of retries
+$api->setDelayFn(function($retries) {
+    return 1000 * pow(2, $retries); // Exponential backoff
+});
+```
+
+### Logging
+
+```php
+use Monolog\Logger;
+use Monolog\Handler\StreamHandler;
+
+$logger = new Logger('google-api');
+$logger->pushHandler(new StreamHandler('php://stdout'));
+
+$api = RestApi::createWithServiceAccount(
+    $serviceAccountConfig,
+    $scopes,
+    $logger
+);
+```
+
+### Custom HTTP Options
+
+```php
+$response = $api->request('/endpoint', 'POST', [
+    'Content-Type' => 'application/json'
+], [
+    'json' => ['key' => 'value'],
+    'timeout' => 30
+]);
+```
+
+## Testing
+
+```bash
+# OAuth tests (require environment variables)
+export CLIENT_ID="your-client-id"
+export CLIENT_SECRET="your-client-secret"
+export REFRESH_TOKEN="your-refresh-token"
+
+# Service Account tests (optional)
+export SERVICE_ACCOUNT_JSON='{"type":"service_account","project_id":"your-project",...}'
+
+# Run tests
+composer tests
+```
+
+## Requirements
+
+- PHP ^7.1
+- guzzlehttp/guzzle ^6.0
+- google/auth ^1.26
 
 ## License
 
-MIT licensed, see [LICENSE](./LICENSE) file.
+MIT