Update README.md

added new api

Author: apilayer-admin

README.md

@@ -968,6 +968,7 @@ API | Description | Auth | HTTPS | CORS |
 | [IPGEO](https://api.techniknews.net/ipgeo/) | Unlimited free IP Address API with useful information | No | Yes | Unknown |
 | [ipgeolocation](https://ipgeolocation.io/) | IP Geolocation AP with free plan 30k requests per month | `apiKey` | Yes | Yes |
 | [IPInfoDB](https://www.ipinfodb.com/api) | Free Geolocation tools and APIs for country, region, city and time zone lookup by IP address | `apiKey` | Yes | Unknown |
+| [ipstack](https://ipstack.com/) | Locate and identify website visitors by IP address | `apiKey` | Yes | Unknown |
 | [Kakao Maps](https://apis.map.kakao.com) | Kakao Maps provide multiple APIs for Korean maps | `apiKey` | Yes | Unknown |
 | [keycdn IP Location Finder](https://tools.keycdn.com/geo) | Get the IP geolocation data through the simple REST API. All the responses are JSON encoded | `apiKey` | Yes | Unknown |
 | [LocationIQ](https://locationiq.org/docs/) | Provides forward/reverse geocoding and batch geocoding | `apiKey` | Yes | Yes |