Add Polygon (#1855)

README.md

@@ -443,6 +443,7 @@ API | Description | Auth | HTTPS | CORS |
 | [marketstack](https://marketstack.com/) | Real-Time, Intraday & Historical Market Data API | `apiKey` | Yes | Unknown |
 | [Nordigen](https://nordigen.com/en/account_information_documenation/integration/quickstart_guide/) | Connect to bank accounts using official bank APIs and get raw transaction data | `apiKey` | Yes | Unknown |
 | [Plaid](https://plaid.com/) | Connect with users’ bank accounts and access transaction data | `apiKey` | Yes | Unknown |
+| [Polygon](https://polygon.io/) | Historical stock market data | `apiKey` | Yes | Unknown |
 | [Razorpay IFSC](https://ifsc.razorpay.com/) | Indian Financial Systems Code (Bank Branch Codes) | No | Yes | Unknown |
 | [Real Time Finance](https://github.com/Real-time-finance/finance-websocket-API/) | Websocket API to access realtime stock data | `apiKey` | No | Unknown |
 | [Styvio](https://www.Styvio.com) | Realtime and historical stock data and current stock sentiment | No | Yes | Unknown |