Update v2_to_v3_guide.md

docs/guides/v2_v3_guide/v2_to_v3_guide.md

@@ -10,6 +10,58 @@ and more flexible library than any previous version.
 
 Below are the most notable breaking changes that you would need to update your code to work with V3.
 
+### GatewayIntents
+
+As Discord.NET has upgraded from Discord API v6 to API v9,
+`GatewayIntents` must now be specified in the socket config, as well as on the [developer portal].
+
+```cs
+
+// Where ever you declared your websocket client.
+DiscordSocketClient _client;
+
+...
+
+var config = new DiscordSocketConfig()
+{
+  .. // Other config options can be presented here.
+  GatewayIntents = GatewayIntents.All
+}
+
+_client = new DiscordSocketClient(config);
+
+```
+#### Common intents:
+
+- AllUnprivileged: This is a group of most common intents, that do NOT require any [developer portal] intents to be enabled.
+This includes intents that receive messages such as: `GatewayIntents.GuildMessages, GatewayIntents.DirectMessages`
+- GuildMembers: An intent disabled by default, as you need to enable it in the [developer portal].
+- GuildPresences: Also disabled by default, this intent together with `GuildMembers` are the only intents not included in `AllUnprivileged`.
+- All: All intents, it is ill adviced to use this without care, as it *can* cause a memory leak from presence.
+The library will give responsive warnings if you specify unnecessary intents.
+
+
+> [!NOTE]
+> All gateway intents, their Discord API counterpart and their enum value are listed
+> [HERE](xref:Discord.GatewayIntents)
+
+#### Stacking intents:
+
+It is common that you require several intents together.
+The example below shows how this can be done.
+
+```cs
+
+GatewayIntents = GatewayIntents.AllUnprivileged | GatewayIntents.GuildMembers | ..
+
+```
+
+> [!NOTE]
+> Further documentation on the ` | ` operator can be found
+> [HERE](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/bitwise-and-shift-operators)
+
+[developer portal]: https://discord.com/developers/
+
 ### ReactionAdded Event
 
 The reaction added event has been changed to have both parameters cacheable.