[docs] added info about mongolab to readme
[docs] added info about mongolab to readme

Phanatic/pkgcloud,hacor/pkgcloud,songanbui/pkgcloud,apla/pkgcloud,temka1234/pkgcloud,mdsummers/pkgcloud,DonSchenck/pkgcloud,mcanthony/pkgcloud,Hopebaytech/pkgcloud,dionjwa/pkgcloud,Phanatic/pkgcloud,bunglestink/pkgcloud,andrewsomething/pkgcloud,pkgcloud/pkgcloud