Update keys.md

Added reference to 2.8's SCAN as an alternative to KEYS

Author: itamarhaber

commands/keys.md

@@ -12,7 +12,7 @@ This command is intended for debugging and special operations, such as changing
 your keyspace layout.
 Don't use `KEYS` in your regular application code.
 If you're looking for a way to find keys in a subset of your keyspace, consider
-using [sets][tdts].
+using `SCAN` or [sets][tdts].
 
 [tdts]: /topics/data-types#sets