Added 'Getting a cookie' to cookies.md

Hi, I miss a 'Getting a cookie'  in cookies.md
I asked myself "so it should probably be in...", may seem a bit obvious
but, maybe not.
Merge pull request #84 from mateuspv/beta

Added 'Getting a cookie' to cookies.md
Merge branch 'beta' of github.com:hapijs/hapijs.com into beta