commands: specify cluster mode in scan docstring

In ValkeyCluster, the cursors are returned as a dict of primaries with
names as keys and cursors as values. Mention that in help to avoid
confusion.

Fixes #191

Signed-off-by: Mikhail Koviazin <[email protected]>

Author: Mikhail Koviazin

valkey/commands/core.py

@@ -2997,7 +2997,9 @@ def scan(
     ) -> ResponseT:
         """
         Incrementally return lists of key names. Also return a cursor
-        indicating the scan position.
+        indicating the scan position. In ValkeyCluster, the cursors are returned
+        as a dictionary with the primary node name as the key and the cursor as
+        the value.
 
         ``match`` allows for filtering the keys by pattern