Document usage of MADR in contribution guide

Author: atextor

CONTRIBUTING.md

@@ -20,6 +20,10 @@ Model (SAMM) and supports its use.
 * For discussions specific to development, the preferred way is
   the [developer mailing list](https://accounts.eclipse.org/mailing-list/esmf-dev).
 
+## Architecture Decision Records
+
+Decisions on code and architecture are documented using [Markdown Any Decision
+Records](https://adr.github.io/madr/) in [documentation/decisions/](https://github.com/eclipse-esmf/esmf-aspect-model-editor/tree/main/documentation/decisions).
 ## Branching
 
 We follow