Hope you did not start work on this yet.
It’s already been originally discussed here: Collecting RuuviTag measurements and displaying them with Grafana
PR is here: https://github.com/openhab/openhab2-addons/pull/4913 (note that it required some fixes to bluez bundle as well to detect devices based on manufacturer id)
It’s already working (with some unnecessary logging), final stages of review. I welcome you to give feedback and test it out
UPDATE: the binding has been merged, and will be part of standard openHAB 2.5.0 release. You can probably use 2.5.0-snapshot version as well until then