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

README.md

@@ -14,6 +14,7 @@
 **English**,
 [Español][ES],
 [Français][FR],
+[Galego][GL],
 [Italiano][IT],
 [Kurdi][KU],
 [Mongolian][MN],
@@ -50,6 +51,7 @@
 [ES]:README.es.md
 [FA]:README.fa.md
 [FR]:README.fr.md
+[GL]:README.gl.md
 [GR]:README.gr.md
 [HI_IN]:README.hi_in.md
 [ID]:README.id.md