examples/mongodb/update_add_array.txt
> db.users.update({ name : 'Zorg' }, { $set : { kids: [ { name: 'Joe' } ] } })

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