Fix typos on pt_BR/gittutorial.txt translation

With extra fixes from Thadeu and Carlos as well.

Signed-off-by: André Goddard Rosa <andre.goddard@gmail.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: Carlos R. Mafra <crmafra2@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: andre-rosa