Add reference to architecture diagrams

Refer to architecture diagrams for model, gui and logic packages

High-Level-Documentation.md

@@ -7,6 +7,8 @@ The `model` represents the most important data structures (`BibDatases`, `BibEnt
 We use an event bus to publish events from the `model` to the other layers.
 This allows us to keep the architecture but still react upon changes within the core in the outer layers.
 
+You can view up-to-date diagrams for model, gui, and logic packages [here](https://sourcespy.com/github/jabref/).
+
 
 ## Package Structure
 Permitted dependencies in our architecture are:
@@ -42,4 +44,4 @@ Both GUI and CLI are started via the `JabRefMain` which will in turn call `JabRe
 ![Class Diagram](http://yuml.me/20975ef4)
 
 Visualization as a class diagram: http://yuml.me/20975ef4
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+-->