code: func LoadSystemPatterns(fs billy.Filesystem) (ps []Pattern, err error) {
  	return loadPatterns(fs, systemFile)
  }
docs: // LoadSystemPatterns loads gitignore patterns from from the gitignore file
  // declared in a system's /etc/gitconfig file.  If the ~/.gitconfig file does
  // not exist the function will return nil.  If the core.excludesfile property
  // is not declared, the function will return nil.  If the file pointed to by
  // the core.excludesfile property does not exist, the function will return nil.
  //
  // The function assumes fs is rooted at the root filesystem.