📝 Update README

Author: IgorRosocha

README.md

@@ -1 +1,64 @@
-# OpenGoogleSignInSDK
+# 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.
+
+## Installation
+
+### Swift Package Manager
+
+SDK can be installed using [SPM](https://github.com/apple/swift-package-manager). Just add following line into your `Package.swift`: 
+
+```swift
+.package(url: "https://github.com/AckeeCZ/OpenGoogleSignInSDK.git", .upToNextMajor(from: "1.0.0")),
+```
+
+or use the Xcode `File -> Swift Packages -> Add Package Dependency` and paste the URL of GitHub repository.
+
+## Integration guide
+
+### Add a URL scheme to your project
+
+Google Sign-In flow requires a URL scheme to be added to your project:
+
+1. Open your project configuration, select your app from the **Targets** section, then select the **Info** tab and expand the **URL Types** section.
+2. Click the **+** button, and add your reversed client ID as a URL scheme. The reversed client ID is your client ID with the order of the dot-delimited fields reversed, like on the picture below:
+
+![url-types|OpenGoogleSignInSDK](Resources/url-types.png)
+
+### Set OAuth 2.0 client ID
+
+First, you need to visit [Google API Console](https://console.developers.google.com/apis/credentials?project=_) to obtain OAuth 2.0 client ID of your project. After obtaining the client ID, you need to configure the `clientID` property of `OpenGoogleSignIn` shared instance in your app delegate:
+
+```swift
+func application(_ application: UIApplication,
+                 didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
+  OpenGoogleSignIn.shared.clientID = "YOUR_CLIENT_ID"
+
+  return true
+}
+```
+
+### Handle Sign-In process
+
+To handle Sign-In process, you need to set `OpenGoogleSignInDelegate` and implement the protocol:
+
+```swift
+OpenGoogleSignIn.shared.delegate = self
+
+...
+...
+...
+
+func sign(didSignInFor user: GoogleUser?, withError error: GoogleSignInError?) {
+  // Signed in user or error received here.
+  // Perform any required operations.
+}
+```
+
+## Author
+
+[Ackee](https://ackee.cz) team
+
+## License
+
+OpenGoogleSignInSDK is available under the MIT license. See the LICENSE file for more info.