Fix return type annotation and explain generator usage

Author: Sangeeth62880

README.md

@@ -315,7 +315,7 @@ def email_clients(clients: List[Client]) -> None:
 **Good**:
 
 ```python
-from typing import List
+from typing import Iterator
 
 
 class Client:
@@ -326,19 +326,25 @@ def email(client: Client) -> None:
     pass
 
 
-def get_active_clients(clients: List[Client]) -> List[Client]:
-    """Filter active clients.
-    """
-    return [client for client in clients if client.active]
+def active_clients(clients: Iterator[Client]) -> Iterator[Client]:
+    """Yield only active clients."""
+    return (client for client in clients if client.active)
 
 
-def email_clients(clients: List[Client]) -> None:
-    """Send an email to a given list of clients.
-    """
-    for client in get_active_clients(clients):
+def email_client(clients: Iterator[Client]) -> None:
+    """Send an email to a given list of clients."""
+    for client in active_clients(clients):
         email(client)
+
+**Why this is better:**
+
+Using a generator avoids creating an intermediate list in memory.
+Clients are filtered lazily, which improves performance and scalability
+when working with large collections.
+
 ```
 
+
 Do you see an opportunity for using generators now?
 
 **Even better**