docs: def _os_install(self, package_file):
          """
          take in a dict return a string of docker build RUN directives
          one RUN per package type
          one package type per JSON key
          """
          packages = " ".join(json.load(package_file.open()))
          if packages:
              for packager in self.pkg_install_cmds:
                  if packager in self.context.externalbasis:
                      installer = self.pkg_install_cmds[packager]
              return f"RUN    {installer} {packages}"
          else:
              return ""