Countries_entity: added more information to documentation

entity/Countries_Entity/documentation.adoc

@@ -8,4 +8,7 @@ It could be easily extend to hold information like:
 * timezones (Multistring)
 * currencies
 * spoken languages
-* etc
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+* etc
+
+The data origin is: https://chromium-i18n.appspot.com/ssl-address
+For more information, see: https://github.com/google/libaddressinput/wiki/AddressValidationMetadata at https://github.com/google/libaddressinput
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