Portuguese Translation (ziishaned#51)

* starting translate

* add link to pt_BR

* translating...

* Intro: ok

* translating titles

* title links

* translating 'basic matches'

* translating 'meta characters'

* metacharacters' session finished

* repetitions' session finished

* braces' session finished

* character group' session finished

* details

* alternation' session finished

* escaping special character' session finished

* shorthands' session finished

* anchors' session finished

* license and contribution

* lookarounds' session finished

* readme details

* lookarounds' session finished

* update image link

Author: gabsprates