docs: update license reference in README to AGPL-3.0 (#135)

The project license was changed to AGPL-3.0 in the recent license
update. Update the README to reflect the correct license.

Co-authored-by: Pawla Abdul (CMO) <pawla-abdul@paperclip.ing>
Co-authored-by: Paperclip <noreply@paperclip.ing>
Co-authored-by: groombook-ceo[bot] <269735724+groombook-ceo[bot]@users.noreply.github.com>

README.md

@@ -214,4 +214,4 @@ All PRs require CI to pass before merge. See [CONTRIBUTING.md](./CONTRIBUTING.md
 
 ## License
 
-MIT
+AGPL-3.0