[DOC] architecture additions

docs/architecture/00-index.adoc

@@ -5,8 +5,12 @@
 To know how to build the project, please have a look at the https://github.com/process-analytics/bpmn-visualization-js/blob/master/CONTRIBUTING.md[contributing guide].
 
 
+include::architecture-overview.adoc[]
+
 include::bpmn-internal-model.adoc[]
 
 include::bpmn-parsing.adoc[]
 
+include::mxgraph-integration.adoc[]
+
 include::bpmn-support-how-to.adoc[]

docs/architecture/architecture-overview.adoc

@@ -0,0 +1,9 @@
+=== Architecture Overview
+
+The lib consists on 2 main modules
+
+* parsing: read a BPMN source (xml string) and convert it into its own link:bpmn-internal-model.adoc[internal Model]
+* rendering: display the BPMN diagrams represented by the internal Model, using the https://jgraph.github.io/mxgraph/[mxGraph library]
+
+image::images/architecture/architecture_overview.svg[]
+

docs/architecture/bpmn-support-how-to.adoc

@@ -24,10 +24,10 @@ flow` support (see `ShapeBpmnElementKind` for more details)
 * Add end-to-end tests, mainly to ensure that the new BPMN element is now stored in the `mxGraph model`, see `mxGraph.model.test.ts`.
 * No need to create specific XML tests, the XML parsing is tested globally using BPMN files for various BPMN vendors.
 
-
+[[bpmn-support-howto-elements-rendering]]
 ==== Elements rendering
 
-When inserting an element on the graph, a style is passed to identify the way it will be rendered.
+When inserting an element on the `mxGraph` graph, a style is passed to identify the way it will be rendered.
 
 The https://jgraph.github.io/mxgraph/docs/js-api/files/view/mxStylesheet-js.html[style] is defined and registered in
 `StyleConfigurator`. In particular, it refers to the name of a https://jgraph.github.io/mxgraph/docs/js-api/files/shape/mxShape-js.html[mxShape]