Add all missing docs

PkmnLib.Static/Item.cs

@@ -106,11 +106,25 @@ public interface IItem : INamedValue
     /// </summary>
     ImmutableHashSet<StringKey> Flags { get; }
 
+    /// <summary>
+    /// The effect of the item when used outside of battle.
+    /// </summary>
     ISecondaryEffect? Effect { get; }
+
+    /// <summary>
+    /// The effect of the item when used in battle.
+    /// </summary>
     ISecondaryEffect? BattleEffect { get; }
 
+    /// <summary>
+    /// A set of arbitrary data that can be set on the item.
+    /// </summary>
     IReadOnlyDictionary<StringKey, object?> AdditionalData { get; }
 
+    /// <summary>
+    /// Tries to get additional data from the item. If the data is not present, the value will be null.
+    /// If the data is present, but cannot be converted to the requested type, the value will be null.
+    /// </summary>
     bool TryGetAdditionalData<T>(StringKey key, out T? value);
 
     /// <summary>