Correct Portuguese grammar and phrasing in index.md

[adrianvic]

I've changed the masculine o articles to the feminine article a when referring to Google as the feminine noun empresa. It feels strange to hear o Google instead of a Google to most Portuguese speakers and from my search o Google refers to the company's search engine (mecanismo de pesquisa in Portuguese - masculine)

I've also fixed the typo combara in the section talking about astrosurfing, combat translates to combata.

I'm not familiar with Portugal's Portuguese, I'm open for corrections to keep the post compatible (or at least reasonably understandable) with both languages, however keep in mind that the language slug for this page is pt-BR and I don't know if the maintainers would prefer a dedicated page for pt-PT.

[marcprux]

Thanks!