Add LinkedIn from inactive PR (#1270)

issue #2002 
resolve #1270

README.md

@@ -1017,6 +1017,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Full Contact](https://www.fullcontact.com/developer/docs/) | Get Social Media profiles and contact Information | `OAuth` | Yes | Unknown |
 | [HackerNews](https://github.com/HackerNews/API) | Social news for CS and entrepreneurship | No | Yes | Unknown |
 | [Instagram](https://www.instagram.com/developer/) | Instagram Login, Share on Instagram, Social Plugins and more | `OAuth` | Yes | Unknown |
+| [LinkedIn](https://docs.microsoft.com/en-us/linkedin/?context=linkedin/context) | The foundation of all digital integrations with LinkedIn | `OAuth` | Yes | Unknown |
 | [Meetup.com](https://www.meetup.com/meetup_api/) | Data about Meetups from Meetup.com | `apiKey` | Yes | Unknown |
 | [MySocialApp](https://mysocialapp.io) | Seamless Social Networking features, API, SDK to any app | `apiKey` | Yes | Unknown |
 | [Open Collective](https://docs.opencollective.com/help/developers/api) | Get Open Collective data | No | Yes | Unknown |