Add Ukrainian README and CONTRIBUTING (#903)

* Add: Ukrainian language

* Fix: grammar mistakes

* Fix: grammar mistakes

README.fr.md

@@ -23,6 +23,7 @@
 [Română][RO],
 [Tiếng Việt][VI],
 [Türkçe][TR],
+[Ukrainian][UA],
 [Ελληνικά][GR],
 [Русский][RU],
 [العربية][AR],
@@ -63,6 +64,7 @@
 [RO]:README.ro.md
 [RU]:README.ru.md
 [TR]:README.tr.md
+[UA]:README.ua.md
 [VI]:README.vi.md
 [ZH_CN]:README.zh_cn.md
 [ZH_TW]:README.zh_tw.md