Added support for the --add option to cli.

bin/gh-pages

@@ -13,12 +13,14 @@ program
   .option('-b, --branch <branch>',
       'name of the branch you\'ll be pushing to', 'gh-pages')
   .option('-t, --dotfiles', 'Include dotfiles')
+  .option('-a, --add', 'Only add, and never remove existing files.')
   .parse(process.argv);
 
 ghpages.publish(path.join(process.cwd(), program.dist), {
   branch: program.branch,
   src: program.src,
   dotfiles: !!program.dotfiles,
+  add: !!program.add,
   logger: function(message) {
     console.log(message);
   }