react-native-pdf-light: add sample image (#2322)

Author: alpha0010

react-native-libraries.json

@@ -6011,6 +6011,9 @@
     "githubUrl": "https://github.com/alpha0010/react-native-pdf-viewer",
     "npmPkg": "react-native-pdf-light",
     "examples": ["https://github.com/alpha0010/react-native-pdf-viewer/tree/master/example"],
+    "images": [
+      "https://raw.githubusercontent.com/alpha0010/react-native-pdf-viewer/master/docs/annotation.png"
+    ],
     "ios": true,
     "android": true
   },