[Design Sprint] Add content for documentation landing page (#308)

* Squashed commit of the following:

commit 30ce1ef
Author: Sergio Delgado Rodriguez <[email protected]>
Date:   Tue Feb 6 15:46:57 2024 -0500

    new_GTFS.org_structure (#307)

    Adding new files for new GTFS architecture. This change does not remove the old files.

commit fe496d1
Author: isabelle-dr <[email protected]>
Date:   Tue Feb 6 14:29:31 2024 -0500

    Removing translations (#306)

    * dummy commit

    * Remove translations part one

    * removing translations

    * Make changes based on review

* Add content for spec landing page

* Remove pencil link and add links to spec

docs/documentation/index.md

@@ -1 +1,13 @@
-Placeholder Text
+# General Transit Feed Specification (GTFS)
+
+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.
+
+GTFS consists of two main parts: [GTFS Schedule](https://gtfs.org/documentation/schedule/reference) and [GTFS Realtime](https://gtfs.org/documentation/Realtime/reference).
+
+## GTFS Schedule
+
+GTFS Schedule is a feed specification that defines a common format for static public transportation information. It is composed of a number of text (.txt) files that are contained in a single ZIP file. Each file describes a particular aspect of transit information: stops, routes, trips, fares, etc.
+
+## GTFS Realtime
+
+GTFS Realtime is a feed specification that allows public transportation agencies to provide up-to-date information about current arrival and departure times, service alerts, and vehicle position, allowing users to smoothly plan their trips.