Update style.md
Update style.md

- Cite reasons why we should consider BEM
- Add a hint about naming

Auditors: @cezaraugusto

Test Plan:

diasdavid/browser-laptop,luixxiul/browser-laptop,diasdavid/browser-laptop,diasdavid/browser-laptop,luixxiul/browser-laptop,luixxiul/browser-laptop,luixxiul/browser-laptop,diasdavid/browser-laptop