update readme

crates/sui-indexer-alt/src/README.md

@@ -8,7 +8,7 @@ cargo run --bin sui-indexer-alt -- --database-url {url} indexer --remote-store-u
 ```
 
 ## Pruning
-To enable pruning, the `cp_mapping` pipeline must be enabled. Otherwise, even if pruning logic is
+To enable pruning, the `cp_sequence_numbers` pipeline must be enabled. Otherwise, even if pruning logic is
 configured for a table, the pruner task itself will skip if it cannot find a mapping for the
 checkpoint pruning watermark. Only one committer needs to update this table - it is not necessary
 for every indexer instance to have this pipeline enabled.