introduction.rst: Add short Architecture section

docs/epilog.rst

@@ -18,3 +18,6 @@
 .. _Sphinx: https://www.sphinx-doc.org
 .. _Virtual machine: https://en.wikipedia.org/wiki/Virtual_machine
 .. _APT: http://en.wikipedia.org/wiki/Advanced_Packaging_Tool
+.. _QEMU: https://www.qemu.org/
+
+.. _Client-server model: https://en.wikipedia.org/wiki/Client-server_model

docs/installation.rst

@@ -1,10 +1,9 @@
 Installation
 ============
 
-sdfsd dfgfd dgd
-
 .. include:: package-repositories.rst
 
+
 This aasd safd
 --------------
 

docs/introduction.rst

@@ -10,6 +10,19 @@ Proxmox Backup is an enterprise class client-server backup software,
 specially optimized for `Proxmox Virtual Environment`_ to backup
 :term:`virtual machine`\ s and :term:`container`\ s.
 
+Architecture
+------------
+
+Proxmox Backup uses a `Client-server model`_. The server is
+responsible to store the backup data, and provides an API to create
+backups and restore data. It is also possible to manage disks and
+other resources using this API.
+
+A backup client uses this API to access the backed up data,
+i.e. ``proxmox-backup-client`` is a command line tool to create
+backups and restore data. We also deliver an integrated client for
+QEMU_ with `Proxmox Virtual Environment`_.
+
 
 Main features
 -------------