Add usage documentation and links

Author: Edvinas01

Documentation/README.md

@@ -1 +1,85 @@
-Documentation
+# Documentation
+
+## Game Events
+The library provides two types of game events:
+- `GameEvent` without arguments.
+- `ArgumentGameEvent` which accept arguments.
+
+### Game event assets
+The core of events is game event `ScriptableObject` assets. They store game event listeners and notify them when an event is raised.
+
+To use game events, create an appropriate game event type asset (where _"Argument Name"_ is type of the argument that you are going to be passing to your events):
+- `GameEvent` - _Right Click -> Create -> Game Events -> Game Event_
+- `ArgumentGameEvent` - _Right Click -> Create -> Game Events -> "Argument Name" Game Event_
+
+Event assets can be referenced and raised in scripts directly or used in `UnityEvent` fields:
+```cs
+public class SceneManager : MonoBehaviour
+{
+    // Reference GameEvent directly.
+    [SerializedField]
+    private GameEvent startSceneGameEvent = default;
+
+    // Or inside UnityEvent.
+    [SerializedField]
+    private UnityEvent onStartScene = default;
+
+    private void Start()
+    {
+        if (startSceneGameEvent != null)
+        {
+            startSceneGameEvent.RaiseGameEvent();
+        }
+
+        onStartScene.Invoke();
+    }
+}
+```
+
+### Custom game events
+If you need to define a game event which accepts custom arguments, extend `GameEvents.Generic.ArgumentGameEvent` class:
+```cs
+[CreateAssetMenu(fileName = "CustomGameEvent", menuName = "Game Events/Custom Game Event")]
+public class CustomGameEvent : ArgumentGameEvent<Custom>
+{
+}
+```
+
+In order to enable raising of custom game events from the inspector, create a `CustomEditor` script where the argument fields are going to be drawn. To do so, define an editor script, extend `GameEvents.Generic.ArgumentGameEventEditor` and override `DrawArgumentField(Custom)` . Make sure to place this script under the `Editor` folder:
+```cs
+[CustomEditor(typeof(CustomGameEvent))]
+public class CustomGameEventEditor : ArgumentGameEventEditor<CustomGameEvent, Custom>
+{
+    protected override Custom DrawArgumentField(Custom value)
+    {
+        // Draw Custom value input fields here.
+    }
+}
+```
+
+### Game event listeners
+Game events can be listened to by listener components. To use listeners, you need to create an appropriate listener component:
+- `GameEvent` - _Add Component -> Game Events -> Game Event Listener_
+- `ArgumentGameEvent` - _Add Component -> Game Events -> "Argument Name" Game Event Listener_
+
+Once the component is added, slot in the appropriate `GameEvent` you want the listener to listen to and add your response methods to `onGameEvent` callback via the inspector.
+
+### Custom game event listeners
+Custom game event listeners which accept different arguments can also be created. First of all, create a `UnityEvent` which would accept your `Custom` type:
+```cs
+[Serializable]
+public class CustomEvent : UnityEvent<Custom>
+{
+}
+```
+
+Then, create a custom game event listener which. This can be done by extending `GameEvents.Generic.ArgumentGameEventListener` class.
+```cs
+[AddComponentMenu("Game Events/Custom Game Event Listener")]
+public class CustomGameEventListener : ArgumentGameEventListener<CustomGameEvent, CustomEvent, Custom>
+{
+}
+```
+
+### Examples
+Import the `GameEvents` samples which show how to use game events in various situations.