Add system diagram reference in the documentation

docs/diagrams.rst

@@ -13,3 +13,10 @@
    :align: center
 
    Process Model for the tuning workflow of a spring-mass-damper.
+
+.. drawio-figure:: ../damper/system.drawio
+   :format: svg
+   :page-index: 1
+   :align: center
+
+   Causal Block Diagram for the spring-mass-damper.