[Tails-l10n] Update of initial pages to pt-br

First of all, thank you drebs, for speaking up. We have a big problem
with the tails-l10n-pt-br list: the translations are done and sent to
the list according to the instructions given, but they are never
reviewed or applied to the main website.

I'm willing to keep doing the translations, if I know my efforts won't
go to waste, being never used.

Let me know what I can do to help so we can advance in the translations.