Architecture: add high level view section

- Add very high view
- Add the main building block details and interaction

Signed-off-by: David Morel <david.morel@vates.fr>

docs/architecture.md

@@ -2,6 +2,27 @@
 
 This page contains advanced info regarding XCP-ng architecture.
 
+## High level view
+
+Here you can find a high level view of how XCP-ng is interacted with by users and other applications, as well as the various blocks that it is made of. This part follows the [c4 model](http://c4model.com) principle for its diagrams.
+
+### Interactions
+
+The Hypervisor runs on a host, and is managed by its user directly via CLI, or through other administration applications such as [Xen Orechestra](https://xen-orchestra.com/#!/xo-home)j or [XCP-ng Center](https://github.com/xcp-ng/xenadmin)
+![c4 system context diagram of XCP-ng](../assets/img/architecture/C1-context-driagram.drawio.png)
+
+### Main Building Blocks
+
+Inside the hypervisor, there are various parts allowing its main features:
+- Controlling and configuring XCP-ng
+- Controlling and configuring the VMs
+- Making network and Storage work for the host and guests
+- Fetching information about the host and the guests
+
+Here is how they organize and interface with each others:
+
+![c4 container diagram of XCP-ng](../assets/img/architecture/C2-xcp-ng-container-diagram.drawio.png)
+
 ## Storage
 
 ### Virtual disks on HVMs and PV guests