Atualização do Readme.md com correções gramáticais

[leticiacamposs2]

Changes in this pull request:

[magul]

Hi @leticiacamposs2, first of all, thanks for your contribution here!

We tend also to maintain translation on Crowdin (Portuguese translation is here: https://crowdin.com/project/django-girls-tutorial/pt-BR#), can you, please, apply your changes also there?

Thanks in advance!