Would you mind elaborating on

  from those to tasks (those are in MD too)

We're doing the design docs in MD thing, but are you saying you've gone a step further and have the backlog represented in git too?

Not the whole backlog, just the tasks for the feature being designed, like an epic. Atlassian has a CLI that - acli. We use Jira as usual, it's just a way to not having to manually propagate design adjustments to Jira.