add architecture diagrams

Author: tomkralidis

docs/architecture/README.md

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+# Architecture diagrams
+
+The architecture diagrams in this directory are designed using the [C4 model](https://c4model.com) for visualising software architecture.
+
+The diagrams are saved as an editable .png file, for easy default viewing on GitHub, showing the last active diagram when saved. Any PNG
+viewer will also render the diagram in the same way. The diagrams can be updated using [diagrams.net](https://diagrams.net).