Review intro.

documentation/usage-guide/intro.md → documentation/usage-guide/intro.rst

-# Introduction
+Introduction
+============
 
 This is the Usage Guide of the View Server (VS). The intended readers are users
-of the web client and external services provided by the View Server.
+of the web client shown below and external services provided by the View Server.
 
 These provided external services are services for searching, viewing, and
-downloading of Earth Observation (EO) data. Services optimized for performance
-as well as for flexibility are provided alongside each other.
+downloading of Earth Observation (EO) data. Services endpoints optimized for
+performance as well as for flexibility are provided alongside each other.
+
+.. figure:: images/webclient_start.*
+   :alt: Web Client
+
+   *Web Client*