Portugese translation 🇵🇹

Translation of the main content in Portugese.

Reference: https://github.com/teivah/100-go-mistakes/blob/master/docs/index.md

Example: Japanese translation https://github.com/teivah/100-go-mistakes/blob/master/docs/ja.md

Advice: Step-wise approach (TL;DR blocks first, then the main content)