Add missing states and xmldoc for all states' purposes

osu.Game/Online/RealtimeMultiplayer/MultiplayerUserState.cs

@@ -5,11 +5,51 @@ namespace osu.Game.Online.RealtimeMultiplayer
 {
     public enum MultiplayerUserState
     {
+        /// <summary>
+        /// The user is idle and waiting for something to happen (or watching the match but not participating).
+        /// </summary>
         Idle,
+
+        /// <summary>
+        /// The user has marked themselves as ready to participate and should be considered for the next game start.
+        /// </summary>
         Ready,
+
+        /// <summary>
+        /// The server is waiting for this user to finish loading. This is a reserved state, and is set by the server.
+        /// </summary>
+        /// <remarks>
+        /// All users in <see cref="Ready"/> state when the game start will be transitioned to this state.
+        /// All users in this state need to transition to <see cref="Loaded"/> before the game can start.
+        /// </remarks>
         WaitingForLoad,
+
+        /// <summary>
+        /// The user's client has marked itself as loaded and ready to begin gameplay.
+        /// </summary>
         Loaded,
+
+        /// <summary>
+        /// The user is currently playing in a game. This is a reserved state, and is set by the server.
+        /// </summary>
+        /// <remarks>
+        /// Once there are no remaining <see cref="WaitingForLoad"/> users, all users in <see cref="Loaded"/> state will be transitioned to this state.
+        /// At this point the game will start for all users.
+        /// </remarks>
         Playing,
+
+        /// <summary>
+        /// The user has finished playing and is ready to view results.
+        /// </summary>
+        /// <remarks>
+        /// Once all users transition from <see cref="Playing"/> to this state, the game will end and results will be distributed.
+        /// All users will be transitioned to the <see cref="Results"/> state.
+        /// </remarks>
+        FinishedPlay,
+
+        /// <summary>
+        /// The user is currently viewing results. This is a reserved state, and is set by the server.
+        /// </summary>
         Results,
     }
 }