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core/agents/README.md

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+This folder abstracts metadata lookup into "agents". Each agent can be implemented to get as
+much info as the external source provides, by using a granular set of interfaces 
+(see [interfaces](interfaces.go)).
+
+A new agent must comply with these simple implementation rules:
+1) Implement the `AgentName()` method. It just returns the name of the agent for logging purposes.
+2) Implement one or more of the `*Retriever()` interfaces. That's where the agent's logic resides.
+3) Register itself  (in its `init()` function).
+
+For an agent to be used it needs to be listed in the `Agents` config option (default is `"lastfm,spotify"`). The order dictates the priority of the agents
+
+For a simple Agent example, look at the [local_agent](local_agent.go) agent source code.