fix for missing image, docs Makefile, and netlify build commands

[jputrino]

Proposed changes

Describe the use case and detail of the change. If this PR addresses an issue on GitHub, make sure to include a link to that issue here in this description (not in the title of the PR).

• This PR restores a missing image to the How NIC Works doc:
  
• fixes the path used in the docs Makefile when running the hugo server locally
• fixes the netlify build command for deploy previews and branch deploys

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto master
• I will ensure my PR is targeting the master branch and pulling from my branch from my own fork