Update docs - bind .dockleignore to dockler container

[oupfiz5]

Could you update docs for using .dockleignore from docker:

...
  VERSION=$(
      curl --silent "https://api.github.com/repos/goodwithtech/dockle/releases/latest" | \
          grep '"tag_name":' | \
          sed -E 's/.*"v([^"]+)".*/\1/' \
         ) && docker run --rm \
                         -v /var/run/docker.sock:/var/run/docker.sock \
                         -v $(pwd)/.dockleignore:/.dockleignore \
                         goodwithtech/dockle:v"${VERSION}" 
...