Add Wallhaven.cc (#1100)

README.md

@@ -699,6 +699,7 @@ API | Description | Auth | HTTPS | CORS |
 | [PlaceKitten](https://placekitten.com/) | Resizable kitten placeholder images | No | Yes | Unknown |
 | [ScreenShotLayer](https://screenshotlayer.com) | URL 2 Image | No | Yes | Unknown |
 | [Unsplash](https://unsplash.com/developers) | Photography | `OAuth` | Yes | Unknown |
+| [Wallhaven](https://wallhaven.cc/help/api) | Wallpapers | `apiKey` | Yes | Unknown |
 
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