add hud string method and code docs for modifiers

MiraAPI.Example/Modifiers/CaptainModifier.cs

@@ -7,6 +7,7 @@ namespace MiraAPI.Example.Modifiers;
 public class CaptainModifier : GameModifier
 {
     public override string ModifierName => "Captain";
+
     public override int GetAmountPerGame()
     {
         return 1;
@@ -16,4 +17,4 @@ public class CaptainModifier : GameModifier
     {
         return 100;
     }
-}
+}

MiraAPI.Example/Modifiers/Freezer/FreezeModifier.cs

@@ -14,7 +14,7 @@ public class FreezeModifier : TimedModifier
 
     public override void OnActivate()
     {
-        if (Player.AmOwner)
+        if (Player?.AmOwner == true)
         {
             Player.moveable = false;
         }
@@ -22,7 +22,7 @@ public class FreezeModifier : TimedModifier
 
     public override void OnTimerComplete()
     {
-        if (Player.AmOwner)
+        if (Player?.AmOwner == true)
         {
             Player.moveable = true;
         }