We are using Slate to power our RPC documentation. If you are changing a comment, make sure to copy the resulting changes to the slate repo and make a PR there as well. For generating markdown use:
go get github.com/melekes/godoc2md
godoc2md -template rpc/core/doc_template.txt github.com/tendermint/tendermint/rpc/core | grep -v -e "pipe.go" -e "routes.go" -e "dev.go" | sed 's$/src/target$https://github.com/tendermint/tendermint/tree/master/rpc/core$'