data routing: update summary page

Add overview and descriptions of Application Services and Output Streams

Signed-off-by: Mike Szczys <mike@golioth.io>

Author: szczys

docs/data-routing/README.md

@@ -4,7 +4,25 @@ slug: /data-routing
 sidebar_position: 0
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-This is a new section that discusses cloud-side control of data from your device
-fleet. You will find information on accessing the data your devices have sent to
-the Golioth servers, and connecting that data to external platforms like
-InfluxDB, MondoDB, AWS, Azure, GCP.
+## Overview
+
+Data Routing is how you can get data from your IoT fleet to where you need it.
+
+While you can use the Golioth web console to view, search, and sort the data
+coming into your devices, most customers also need to connect their data to
+existing databases, business logic, or user apps. Golioth is built for this!
+
+## Application Services
+
+Our application services detail how to work with stateful (LightDB State) and
+time-series (LightDB Stream) fleet data. These pages focus on using the
+`goliothctl` and `coap` [command-line
+tools](/reference/command-line-tools/tutorial/). You will likely find this
+section useful during active development.
+
+## Output Streams
+
+Output Streams are integrations with popular services like cloud servers,
+database platforms, and visualization engines. These pages include detailed
+guides on how to connect your Golioth accounts to these services so that incoming
+device data immediately passes through Golioth and arrives where you need it.