Mount volume main repository folder

[avelino]

You must mount the repository volume

We don't usually use github actions to run standalone commands like echo

[addnab]

The README does have it documented here. Sorry if it wasn't clear. Feel free to suggest any improvements to the docs.

- uses: addnab/docker-run-action@v1
  with:
    image: docker:latest
    options: -v $GITHUB_WORKSPACE:/work -e ABC=123
    run: |
      echo "first line"

[addnab]

Updated the README with the typical use case and moved it to the top.