chore: adding a single player session section

com.unity.netcode.gameobjects/Documentation~/TableOfContents.md

@@ -18,6 +18,7 @@
     * [Connection approval](basics/connection-approval.md)
     * [Max players](basics/maxnumberplayers.md)
   * [Transports](advanced-topics/transports.md)
+  * [Single player sessions](advanced-topics/singleplayer.md)
   * [Unity Relay](relay/relay.md)
   * [Command-line arguments](command-line-arguments.md)
 * [Network components](network-components.md)

com.unity.netcode.gameobjects/Documentation~/advanced-topics/singleplayer.md

@@ -0,0 +1,71 @@
+# Single player sessions
+
+Netcode for GameObjects provides a [SinglePlayerTransport](https://docs.unity3d.com/Packages/com.unity.netcode.gameobjects@2.13/api/Unity.Netcode.Transports.SinglePlayer.SinglePlayerTransport.html) which derives from [NetworkTransport](https://docs.unity3d.com/Packages/com.unity.netcode.gameobjects@2.13/api/Unity.Netcode.NetworkTransport.html).
+
+This provides the ability to run a hosted session using the single player transport without having to modify your primary netcode script.
+
+## Adding the single player transport
+
+- Add the `SinglePlayerTransport` to your NetworkManager.
+- You can create a custom `MonoBehaviour` component to handle your connection flow or you can derive from `NetworkManager` and add additional methods/logic to handle starting a single player session or multiplayer session.
+  - When starting a single player session, prior to starting the NetworkManager as a host (_required_), you will want to assign the `SinglePlayerTransport` to the `NetworkManager.NetworkConfig.NetworkTransport`.
+  - When starting a multiplayer session, prior to starting the NetworkManager, you will want to assign the `UnityTransport` (_or any other `NetworkTransport` derived class that you might use for multiplayer sessions_) to the `NetworkManager.NetworkConfig.NetworkTransport`.
+
+## Example script
+
+Below is an example script that derives from NetworkManager to provide a single method to start a single or multi player session:
+
+```csharp
+using Unity.Netcode;
+using Unity.Netcode.Transports.SinglePlayer;
+using Unity.Netcode.Transports.UTP;
+
+/// <summary>
+/// Example of how to start a single player or multiplayer session.
+/// </summary>
+public class ExtendedNetworkManager : NetworkManager
+{
+    public enum StartType
+    {
+        SinglePlayer,
+        Client,
+        Host,
+        Server
+    }
+
+    private UnityTransport m_UnityTransport;
+    private SinglePlayerTransport m_SinglePlayerTransport;
+
+    private void Awake()
+    {
+        m_UnityTransport = GetComponent<UnityTransport>();
+        m_SinglePlayerTransport = GetComponent<SinglePlayerTransport>();
+    }
+
+    public bool StartSession(StartType startType)
+    {
+        var startStatus = false;
+        NetworkConfig.NetworkTransport = startType == StartType.SinglePlayer ? m_SinglePlayerTransport : m_UnityTransport;
+        switch (startType)
+        {
+            case StartType.Host:
+            case StartType.SinglePlayer:
+                {
+                    startStatus = StartHost();
+                    break;
+                }
+            case StartType.Server:
+                {
+                    startStatus = StartServer();
+                    break;
+                }
+            case StartType.Client:
+                {
+                    startStatus = StartClient();
+                    break;
+                }
+        }
+        return startStatus;
+    }
+}
+```