Update index.md

mostly的翻译由“只要”改为“主要”，并修改部分词语让句子更通顺。
Replaces & x &amp;
Replaces cellspacing='0' cellpadding='0' border='0' x css alternatives
Adds css for #subscriptions-form table
fix typo.
2.1.0-preview1 -> 2.1.0-preview2
Added summary sections, small translation fixes (ru)
Latest news translated (ru)
Merge pull request #397 from muryoimpl/fix-typo-news-2013-11-22-ruby-2-1-0-preview2-is-released

Fix typo in ja/news/_post/2013-11-22-ruby-2-1-0-preview2-is-released.md.
Merge pull request #399 from gazay/small-fixes

Added summary sections, small translation fixes (ru)
Merge pull request #398 from gazay/ru-latest-news

Latest news translated (ru)
Fix typo in Ruby 2.1.0-preview2 post (ru)
Update gem bundle (jekyll 1.3.1)
Split first paragraph on mailing-lists page (en)
Emphasize first paragraphs (except for ko, ja, zh_*)
Fix typos
Translate Russian Translation (zh_tw).
Merge pull request #401 from evilexp/patch-1

Fix typos (ru)
Merge pull request #389 from jazzi/master

Update index.md
Merge pull request #387 from murtra/html_fixes

Html fixes
HTML fixes (replace '&' by '&amp;')