Add tip to documentation

doc/iterative_cleanup.md

@@ -199,6 +199,8 @@ data back into the migration, and identifying whether a given value in
 subsequent worksheet iterations has been previously included in a
 worksheet.
 
+**TIP**: You can add the `:fingerprint` by defining a `base_job_cleaned_pre_xforms` method in your cleanup module config. I've done this in several kiba-tms cleanup configs where the base tables are generated by other complicated automated processes, where it'd be a nightmare to work in the addition of the fingerprint field. See [Kiba::Tms::AltNumsForRefmasterTypeCleanup](https://github.com/lyrasis/kiba-tms/blob/main/lib/kiba/tms/alt_nums_for_refmaster_type_cleanup.rb) as an example.
+
 #### Required before extending `IterativeCleanup`: `fingerprint_fields`
 
 The fields that will be hashed into the `:clean_fingerprint` value.