Update README.md

Co-authored-by: Jan Mísař <jan.misar@ackee.cz>

Author: IgorRosocha

README.md

@@ -1,6 +1,6 @@
 # OpenGoogleSignInSDK
 
-OpenGoogleSignInSDK is an open-source library which takes care of Google Sign-In flow using OAuth 2.0 and can be used as an alternative to GoogleSignIn SDK.
+OpenGoogleSignInSDK is an open-source library which takes care of Google Sign-In flow using OAuth 2.0 and can be used as an alternative to [official GoogleSignInSDK](https://developers.google.com/identity/sign-in/ios/sdk).
 
 ## Installation
 
@@ -61,4 +61,4 @@ func sign(didSignInFor user: GoogleUser?, withError error: GoogleSignInError?) {
 
 ## License
 
-OpenGoogleSignInSDK is available under the MIT license. See the LICENSE file for more info.
+OpenGoogleSignInSDK is available under the MIT license. See the LICENSE file for more info.