解决方法@H_404_6@

> gem help rdoc

Usage: gem rdoc [args] [options]
Options:
      --all                        Generate RDoc/RI documentation for all
                                   installed gems
      --[no-]rdoc                  Include RDoc generated documents
      --[no-]ri                    Include RI generated documents
  -v,--version VERSION            Specify version of gem to rdoc
Arguments:
  GEMNAME       gem to generate documentation for (unless --all)
Summary:
  Generates RDoc for pre-installed gems
Defaults:
  --version '>= 0' --rdoc --ri