Add game invite image (discord#7843)

Author: anthonydiscord

docs/discord-social-sdk/development-guides/managing-game-invites.mdx

@@ -218,6 +218,8 @@ client->SendActivityInvite(targetUserId, inviteMessage, [](discordpp::ClientResu
 });
 ```
 
+![Example of a sent game invite in the Discord client](images/social-sdk/development-guides/game-invite.webp)
+
 ---
 
 ## Receiving Game Invites