How to subscribe to generic external MQTT topics?

Thank you and congratulations with GREAT ESP8266 IoT-framework!

I am running a MQTT-broker publishing various topics with information (RSS-feeds, data from different wireless units and running scripts etc.)

Question: what is the optimal way of using Homie for subscribing to topics not under the Homie notation? F.ex. how can I subscribe to regular published messages from my MQTT broker on the topic “/price/oil” published from a python script collecting data on the web?

[Excuse me if this is a trivial question]

best regards,