Windows compatibility

If you use Windows or you want developers on Windows to use your project, add this to your Gemfile.

From the file created by jekyll new for Jekyll 4.1.

• Gemfile

    # Windows and JRuby does not include zoneinfo files, so bundle the tzinfo-data gem
    # and associated library.
    platforms :mingw, :x64_mingw, :mswin, :jruby do
      gem "tzinfo", "~> 1.2"
      gem "tzinfo-data"
    end
  
    # Performance-booster for watching directories on Windows
    gem "wdm", "~> 0.1.1", :platforms => [:mingw, :x64_mingw, :mswin]