Update "Introduction to Bitcoin" in Spanish

[nikosbentenitis]

The "Introduction to Bitcoin" article in Spanish needs to be reviewed for grammar and style. Issue is assigned to @cesgon but @ABISprotocol contribute if you are able.

[sebaslogen]

Hola Nikos, I can also help with the Spanish translations, I just sent a review for half of this issue.
If you need help with more translations you can assign me some.

[ABISprotocol]

Gracias, @neoranga55. Espero que podemos seguir colaborando.