Added galician CONTRIBUTING and README files (#811)

* docs: add Galician README

* docs: fixed country code

* docs: add Galician CONTRIBUTING

* docs: add Galician to CONTRIBUTING language list

* docs: add Galician to README language list

* docs: fixed translation error

* docs: fix trailing space l:104

* docs: fix translation

* docs: fix untranslated quote

* docs: fix sentence without translation