Improve README for Spanish codes

[gdalmau]

Description

Improve README for Spanish codes:

• CIF: Certfiticado --> Código
• CUPS (Código Unificado de Punto de Suministro): literal translation is "Supply Point Unified Code" but the actual name in English is "Meter Point Administration Number"
• DNI: capitalized names standing for each letter
• NIE: Número de Identificación de Extranjeros --> Extranjero

Documentation

• CIF: https://es.wikipedia.org/wiki/C%C3%B3digo_de_identificaci%C3%B3n_fiscal
• CUPS:
  • Spanish: https://es.wikipedia.org/wiki/C%C3%B3digo_Unificado_de_Punto_de_Suministro
  • English: https://en.wikipedia.org/wiki/Meter_Point_Administration_Number
• NIE: https://es.wikipedia.org/wiki/N%C3%BAmero_de_identidad_de_extranjero

[arthurdejong]

Hi Gerard,

Thanks for the improvements. I've merged them with some changes as 7f3dcf0 because the README is generated from the docstrings on release (so are a few other places see update/numlist.py).

Thanks!