We recently added more documentation that may be helpful for developers who are either currently building or thinking about building a Hummingbot connector:
Adding connectors: overview, list of templates, file structure, guidelines
Adding connectors to other blockchains: we added some initial documentation around this. Note that we first have to do some foundational architecture work in order to support non-Ethereum blockchains; afterwards, external developers will be able to add more connectors. We expect to finish this work before end of Q4 2019.
Order lifecycle: explanation of how an order is handled as it transitions to various states in its lifecycle. When implementing a new connector, please take care must be taken to ensure all the order status updates and emitted events adhere to the same semantics as other connectors.
For what additional topics would you like to see documentation? What questions do you have wrt building connectors?