Update SPM instructions (#120)

Author: Widcket

README.md

@@ -62,17 +62,17 @@ Then run `carthage bootstrap --use-xcframeworks`.
 
 If you are using the Swift Package Manager, open the following menu item in Xcode:
 
-**File > Swift Packages > Add Package Dependency...**
+**File > Add Packages...**
 
-In the **Choose Package Repository** prompt add this url: 
+In the **Search or Enter Package URL** search box enter this url: 
 
 ```
 https://github.com/auth0/SimpleKeychain.git
 ```
 
-Then, press **Next** and complete the remaining steps.
+Then select the dependency rule and press **Add Package**.
 
-> For more information on SPM, check [its official documentation](https://developer.apple.com/documentation/xcode/adding_package_dependencies_to_your_app).
+> For further reference on SPM, check [its official documentation](https://developer.apple.com/documentation/swift_packages/adding_package_dependencies_to_your_app).
 
 ## Usage