adds how this works section

README.md

@@ -44,19 +44,21 @@ It creates the following reports:
 + `{library}-unique-reserveid-sierra.csv` (temp, work file)
 
 Actionable reports have the `FINAL` affix in the title.
+
 `FINAL-duplicate-reserveid-sierra.csv` provides information on discovered in the ILS duplicates based on OverDrive Reserve ID.
-`FINAL-for-deletion-verified-resources.csv` provides a list of records that can be deleted from ILS because the library no longer have access to the resource or because OverDrive removed the resource from their catalog.
-`Final-for-import-missing-resources.csv` provides a list of Reserve IDs that can be used to create a MARC file in OverDrive Marketplace that can be used to add these resources to the ILS.
 
-`false-positive-for-deletion.csv` includes resources that were not present in the SimplyE database, but were discovered in the ILS and an alternative verification (webscraping of OverDrive catalog - see details below) found that in fact they are available to our patrons. This report should be shared with SimplyE devs to mitigate missing in SimplyE titles.
+`FINAL-for-deletion-verified-resources.csv` provides a list of records that can be deleted from ILS because the library no longer have access to the resource or because OverDrive removed the resource from their catalog. Please take extra precautions deleting records from Sierra. It is possible that occasionally an item record belonging to a print version of the resource is attached to electronic resource bib in Sierra. In such cases a new record for print must be first brought from WorldCat, then item transfered to it before the electronic resource bib can be deleted.
 
-### how this works?
+`Final-for-import-missing-resources.csv` provides a list of Reserve IDs that can be used to create a MARC file in OverDrive Marketplace that can be used to add these resources to the ILS.
 
-[![diagram](https://github.com/BookOps-CAT/overdrive-reconcile/blob/main/docs/media/Overdrive-weeding.drawio.png)](https://github.com/BookOps-CAT/overdrive-reconcile/blob/main/docs/media/Overdrive-weeding.drawio.png)
+`false-positive-for-deletion.csv` includes resources that were not present in the SimplyE database, but were discovered in the ILS and the verification routine (webscraping of OverDrive catalog - see details below) found that in fact they are available to our patrons. This report should be shared with SimplyE devs to mitigate missing in SimplyE titles.
 
-### verifying deletion list
+### how this works?
 
+The script analysis OverDrive data pulled from ILS (Sierra) and compares it with data pulled from SimplyE database. These two sets acquire information from two different sources: OverDrive Marketplace MARC records and OverDrive API. Resources found in both sets are considered to be available and are left alone. Identification of resources found in the SimplyE database only allow compilation of a MARC file in the OverDrive Marketplace so they are ingested into ILS. Resources found only in Sierra may indicate they are no logger available from OverDrive. This however needs to be verified because of OverDrive API crashes ([SIMPLY-391 issue](https://jira.nypl.org/browse/SIMPLY-3961)) that result in missing data in SimplyE DB. 
 
+[![diagram](https://github.com/BookOps-CAT/overdrive-reconcile/blob/main/docs/media/Overdrive-weeding.drawio.png)](https://github.com/BookOps-CAT/overdrive-reconcile/blob/main/docs/media/Overdrive-weeding.drawio.png)
 
+The verification process of missing in Sierra resources is done via web scraping of OverDrive catalog (we do not have access to OverDrive API to do it more efficiently).
 
 ### changelog