Update index.md

Updated some outdated link and description, corrected some typo, and made the translation from english more fluent.
Update ruby-core page (it)

Update translation (now pertinent to the EN ruby-core page), fix some typo, add How to use GitHub.
Update ruby-core page (it) (fixed)

Update translation (now pertinent to the EN ruby-core page), fix some typo, add How to use GitHub.
Corrected types and missing commas (ru).
Added a translation for the Logo page (ru).
Added a translation for the site footer (ru).
Update weblogs page (it) (link ref fixed)

correct some typo, clean a broken link, link references synced to en
Fix mirror sites URLs in en
Fix mirror sites URLs in ja
Add missing newline in quickstart code sample

Noticed this as I was going through it, would be better to have a newline here.
Merge pull request #559 from cluk3/patch-8

Update weblogs page (it)
Merge pull request #551 from cluk3/patch-5

Update ruby-core page (it)
Merge pull request #548 from cluk3/patch-2

Update user-groups page (it)
Merge pull request #555 from arbox/fb_news_maintenance

Corrected typos and missing commas (ru).
Merge pull request #557 from arbox/fb_rubylogo

Added a translation for the Logo page (ru).
Merge pull request #558 from arbox/fb_sitefooter

Added a translation for the site footer (ru).
Merge pull request #562 from btakashi/patch-1

Add missing newline in quickstart code sample