Added Pexels API (#952)

README.md

@@ -678,6 +678,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Gyazo](https://gyazo.com/api/docs) | Upload images | `apiKey` | Yes | Unknown |
 | [Imgur](https://apidocs.imgur.com/) | Images | `OAuth` | Yes | Unknown |
 | [Lorem Picsum](https://picsum.photos/) | Images from Unsplash | No | Yes | Unknown |
+| [Pexels](https://www.pexels.com/api/) | Free Stock Photos and Videos | `apiKey` | Yes | Yes |
 | [Pixabay](https://pixabay.com/sk/service/about/api/) | Photography | `apiKey` | Yes | Unknown |
 | [Pixhost](https://pixhost.org/api/index.html) | Upload images, photos, galleries | No | Yes | Unknown |
 | [PlaceKitten](https://placekitten.com/) | Resizable kitten placeholder images | No | Yes | Unknown |