Document grype-version parameter

[vprivat-ads]

No description provided.

[spiffcs]

Thanks @vprivat-ads - looks like we need the DCO to run for this. Can you sign off your commits?

To add your Signed-off-by line to every commit in this branch:

    Ensure you have a local copy of your branch by [checking out the pull request locally via command line](https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/checking-out-pull-requests-locally).
    In your local branch, run: git rebase HEAD~1 --signoff
    Force push your changes to overwrite the branch: git push --force-with-lease origin patch-1

[vprivat-ads]

Done

[kzantow]

Thanks for the contribution. Sorry for the delay!