Siegfried homebrew error

[ross-spencer]

Hi Misty - reviewing the Siegfried Wiki today to update some install instructions, I notice the original homebrew command will no longer work - I believe with the change in golang module handling a short while back.

The error I am seeing in Linuxbrew is:

github.com/richardlehane/siegfried/cmd/sf

no required module provides package github.com/richardlehane/siegfried/cmd/sf: go.mod file not found in current directory or any parent directory; see 'go help modules'

If reporting this issue please do so at (not Homebrew/brew or Homebrew/core):
  https://github.com/mistydemeo/homebrew-digipres/issues

Richard's branch happens to have an up-to-date recipe so it'd be pretty easy to make a PR across forks, but first wanted to let you know, and second ask what you thought best to do?