add note on how to get an example keycloak setup for the example setup

Makefile

@@ -0,0 +1,7 @@
+verify:
+	mvn -f attribute-endpoints-provider verify
+
+clean:
+	mvn -f attribute-endpoints-provider clean
+
+.PHONY: verify clean

README.md

@@ -12,10 +12,18 @@ Every endpoint responds with a list of all attribute values, that:
 
 Multivalue attributes are flattened in the response.
 
+## Building
+
+Maven is required for building the provider.
+
+Once all dependencies are met, simply call `make` to build the provider, which should then produce a `attribute-endpoints-provider-1.0-SNAPSHOT.jar` in the `attribute-endpoints-provider/target/` directory.
+
+There's also `make clean` available for removing the output directory.
 
 ## Example Setup
 
 We assume an unconfigured, fresh Keycloak installation running under `http://localhost:8080`.  
+(This can be achieved by running the provided `compose.yaml` after building the provider as outlined in [Building](#building).)
 
  1. Add a new realm  
     e.g. "TestRealm"