Document link to IANA's language subtags registry

_config.yml

@@ -2,6 +2,9 @@
 markdown: kramdown
 highlighter: rouge
 paginate: 100 # it will paginate after this number
+
+# See subtags listed in the IANA language subtag registry:
+# https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry
 language: 'en'
 
 # edit baseurl to simply '/' if using as your personal page (instead of a project page)