This repo contains a few different ways to streamline posting to Nikola from an iPhone.
All of these use Working Copy as the communication medium. Your process should allow a git push to refresh the hosted version.
The workflow directory contains a Workflow to share links (via Working Copy) from the iOS share sheet.
There are other integrations available to post a full article (via Working Copy's integrations with Editorial or Textastic, but I wanted something more streamlined to share links easily.
This doesn't do the git commit or git push for you. It'd be easy to add those, but doing them manually isn't hard and gives you a chance to make edits.
Direct link to the Workflow (I believe you can install it straight from here): workflow.
More info on how this fits into a process is at b.splendous.net.
From Editorial, it's easy to post by copying or refreshing the file back to Working Copy. That won't create the header, though.
So I've created a small Editorial workflow to either prepend a sample header or refresh the date in an existing one. A direct link to install the workflow into Editorial is below: http://www.editorial-workflows.com/workflow/5827525913608192/UmAEPwA3GZQ