Merge pull request MobilityData#255 from MobilityData/add-gtfs-realti…

…me-prediction-metrics

Add GTFS Realtime prediction metrics

README.md

@@ -493,6 +493,7 @@ Massachusetts Bay Transportation Authority (MBTA)](https://github.com/mbta).
 - [transit-feed-quality-calculator](https://github.com/CUTR-at-USF/transit-feed-quality-calculator) - A Java project that uses the [gtfs-realtime-validator](https://github.com/CUTR-at-USF/gtfs-realtime-validator) to assess the quality of a large number of transit feeds, fetching the feed URLs from a global directory ([TransitFeeds.com/OpenMobilityData.org](https://openmobilitydata.org/)).
 - [Transit Network Model](https://github.com/tmelliott/TransitNetworkModel) - A tool to generate predictions using GTFS-realtime VehiclePositions, a particle filter, and a Kalman Filter. 
 - [GTFS Realtime Display](https://git.wtf-eg.de/dancesWithCycles/gtfs-rt-display) - Analyse, monitor and maintain GTFS Realtime data. [Example instances](https://www.swingbe.de/activity/gtfs-rt-display/)
+- [GTFS Realtime Prediction Accuracy metrics](https://docs.google.com/document/d/1-AOtPaEViMcY6B5uTAYj7oVkwry3LfAQJg3ihSRTVoU/edit#heading=h.j27shba7rlk6) - Useful Performance Metrics for GTFS-Realtime.
 
 ### SIRI