Add documentation link

FreePhoenix888 · FreePhoenix888 · commit 7d55ab4455ea · 2023-07-24T11:53:26.000+06:00
diff --git a/README.md b/README.md
@@ -55,4 +55,6 @@ To receive messages on Client read [Firebase Cloud Messaging Documentation](http
 
 # Library
 ## Library Usage
-See [Documentation] for examples and API
+See [Documentation] for examples and API
+
+[Documentation]: https://deep-foundation.github.io/firebase-push-notification/
