Start of Portuguese Translation

I start translating the docs to portuguese beggining by the user guide.
I read the contributing.md file before start but as this is my first PR on this i ask you please to check if i follow the protocol correctly, and if there is anything incorret tell me so i can solve the problem and do not make the same mistake next time.

At the "Contributing" section of contributing.md there are instruction of how to name the branchs an commits of PR's but this instruction doesn't seens to apply to translations, so if there is any instructions on how to do it on translations feel free to correct me.

Thanks