add GTFS Diff

#229

README.md

@@ -386,6 +386,7 @@ Converters from various static schedule formats to and from GTFS.
 
 - [bus-router](https://github.com/atlregional/bus-router) - Python script that generates missing shapes.txt for GTFS using routing from [Google Maps Directions API](https://developers.google.com/maps/documentation/directions/) or [OSRM](https://github.com/Project-OSRM/osrm-backend/wiki/Server-api).
 - [gtfs-blocks-to-transfers](https://github.com/TransitApp/GTFS-blocks-to-transfers) - A Python tool to convert GTFS blocks, defined by setting [trip.block\_id](https://github.com/google/transit/blob/master/gtfs/spec/en/reference.md#example-blocks-and-service-day) into a series of [trip-to-trip transfers (proposal)](https://github.com/google/transit/pull/303).
+- [GTFS Diff](https://transport.data.gouv.fr/tools/gtfs_diff) - GTFS Diff is a specification created by transport.data.gouv.fr and aims at providing a simple and unified way to express differences between GTFS files.
 - [GTFS Editor](https://github.com/conveyal/gtfs-editor) - A (self-hosted) web-based GTFS editing framework. (Note: this project has been deprecated in favor of [IBI Data Tools](https://github.com/ibi-group/datatools-ui).)
 - [GTFS Editor for Vagrant](https://github.com/laidig/vagrant-gtfs-editor) - Quickly set up the GTFS editor (above) using [Vagrant](https://www.vagrantup.com/)
 - [static-GTFS-manager](https://github.com/WRI-Cities/static-GTFS-manager) - A (self-hosted) browser-based user interface for creating, editing, exporting static GTFS (see [related post](https://groups.google.com/forum/#!topic/transit-developers/GFz5rTJTB0I)).