Update README.md

Author: ledjon-behluli

README.md

@@ -100,6 +100,8 @@ A collection of unique items that preserves their original insertion order. It c
 
 **Useful for:** Tracking a sequence of unique events, processing queue for unique jobs.
 
+> ⚠️ Note that this is an **ordered** collection, not a **sorted** one.
+
 ```csharp
 // Add returns true if the item was new
 if (history.Add("user_logged_in"))
@@ -169,6 +171,8 @@ A one-to-many collection that maps a key to a **unique  set**  of values that ma
 
 **Useful for:** Tracking user achievements in the exact order they were earned, managing ordered unique dependencies for a build system, storing timelines of unique events per entity.
 
+> ⚠️ Note that this is an **ordered** collection, not a **sorted** one.
+
 ```csharp
 // Track the unique products a user viewed, in order.
 lookup.Add(userId, "product-123");