Add more comments around catch up logic

osu.Game/Screens/OnlinePlay/Multiplayer/Spectate/ISpectatorPlayerClock.cs

@@ -17,8 +17,11 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer.Spectate
         Bindable<bool> WaitingOnFrames { get; }
 
         /// <summary>
-        /// Whether this clock is resynchronising to the master clock.
+        /// Whether this clock is behind the master clock and running at a higher rate to catch up to it.
         /// </summary>
+        /// <remarks>
+        /// Of note, this will be false if this clock is *ahead* of the master clock.
+        /// </remarks>
         bool IsCatchingUp { get; set; }
 
         /// <summary>

osu.Game/Screens/OnlinePlay/Multiplayer/Spectate/MultiSpectatorPlayer.cs

@@ -59,6 +59,7 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer.Spectate
 
             protected override void Update()
             {
+                // The SourceClock here is always a CatchUpSpectatorPlayerClock.
                 // The player clock's running state is controlled externally, but the local pausing state needs to be updated to stop gameplay.
                 if (SourceClock.IsRunning)
                     Start();