Update README.md

README.md

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-The repository contains specification to manipulate General Transit
-Feed Specification (GTFS) and GTFS Realtime:
-* [GTFS](/gtfs/README.md)
-* [GTFS Realtime](/gtfs-realtime/README.md)
+# General Transit Feed Specification (GTFS) Overview
+The General Transit Feed Specification (GTFS) is an [Open Standard](https://www.interoperablemobility.org/definitions/#open_standard) used to distribute relevant information about transit systems to riders. It allows public transit agencies to publish their transit data in a format that can be consumed by a wide variety of software applications. Today, the GTFS data format is used by thousands of public transport providers.GTFS consists of two formats: GTFS Schedule and GTFS Realtime.
 
-Please visit https://gtfs.org for information.
+[Read more about GTFS](https://gtfs.org/)
+
+# Get Monthly Updates on GTFS Developments
+The GTFS Digest is a resource generated monthly by [MobilityData](https://mobilitydata.org/) providing an overview of developments on GTFS. 
+
+### **🔔 [Subscribe to the GTFS Digest](https://groups.google.com/g/gtfs-updates)**
+
+GTFS relies on community contributions. Please help us capture GTFS developments by sharing your updates for our next digest to: [specifications@mobiltydata.org](mailto:specifications@mobiltydata.org)
+
+# Useful Resources
+## Getting Started with GTFS
+- Visit [GTFS.org](https://gtfs.org/) to learn more about GTFS
+  - An overview of [GTFS Schedule](https://gtfs.org/schedule/)
+  - An overview of [GTFS Realtime](https://gtfs.org/realtime/)
+
+## Contribute to GTFS and join the Community
+
+- [Learn how you can contribute to GTFS Development](https://github.com/google/transit/blob/master/CONTRIBUTING.md)
+- Join [__Slack__](https://share.mobilitydata.org/slack) and introduce yourself to the community.
+- Join [__GTFS Changes__](https://groups.google.com/g/gtfs-changes) and [__GTFS Realtime__](https://groups.google.com/g/gtfs-realtime) Google Groups to stay informed on development.
+
+
+## What is GitHub? 
+* [Getting Started with GitHub](https://docs.github.com/en/get-started)