examples/mongodb/update_push.txt
> db.users.update({ name : 'Zorg' }, { $push : { kids: { name: 'Marry' } } })

> db.users.find()
{ "_id" : ObjectId("526b8fdba444e81f1ca06ba2"), "name" : "Foo" }
{ "_id" : ObjectId("526b9048a444e81f1ca06ba3"), "name" : "Zorg",
     "kids" : [ { "name" : "Joe" }, { "name" : "Marry" } ] }
{ "_id" : ObjectId("526ba048a444e81f1ca06ba4"), "name" : "Moo" }