Add a small README

README.md

+feedback-loop
+===
+
+
+This small server receives spam feedback loop messages, as sent from
+large email providers in ARF format, and stores the entries in a
+database so that you can see aggregates and details via a web
+interface. Records are periodically expunged from the database if they
+are older than a certain time period.
+
+Due to the common tendency to report mailing list emails as spam, the
+tool tries to identify reports for mailing lists emails, and presents
+their statistics separately from those about emails from ordinary
+users (which are often indicative of an account takeover). Details
+(i.e. the message body) for mailing list emails are not saved to the
+database to save space and effort.
+