setup.md: Document external requirements
Solves: Jira GER-2365
Change-Id: Ibbc6d45a7d01a92df6b17d2272f47f8eb08e6654
diff --git a/src/main/resources/Documentation/setup.md b/src/main/resources/Documentation/setup.md
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+# Setting up events-eiffel
+
+## Requirements
+
+### Publishing
+Infrastructure to which the events can be posted.
+
+Supported:
+* [RabbitMQ](https://www.rabbitmq.com/)
+
+### Event consistency
+To ensure consistency with previously published events the plugin needs access
+to the following eiffel event repository APIs:
+* [Eiffel GraphQL API](https://github.com/eiffel-community/eiffel-graphql-api).
+* [Eiffel GoER](https://github.com/eiffel-community/eiffel-goer)
+
+This can be bypassed by setting `EventIdCache.trustLocalCache = True`.
+Setting this means the local Gerrit cache of published events is taken as the
+truth and the Eiffel Repostory APIs aren't necessary. The side-effect is that
+inconsistencies may follow if events are sent by others than the events-eiffel
+plugin.
