Fix cleanup_on_start README

Co-authored-by: Daniel Jaglowski <[email protected]>

Author: pandres-varian

extension/storage/filestorage/README.md

@@ -35,7 +35,7 @@ The default timeout is `1s`.
 A value of zero will ignore transaction sizes.
 
 `compaction.cleanup_on_start` (default: false) - specifies if removal of compaction temporary files is performed on start.
-It will remove all the files in the compaction directory starting with tempdb,
+It will remove all temporary files in the compaction directory (those which start with `tempdb`),
 temp files will be left if a previous run of the process is killed while compacting.
 
 ### Rebound (online) compaction