Update README

Author: Mawuli Adzaku

.gitignore

@@ -4,3 +4,5 @@
 /docs
 erl_crash.dump
 *.ez
+
+/doc

README.md

@@ -8,8 +8,52 @@ Elixir library for validating credit card numbers (a port of [credit_card_valida
 
 ## Documentation
 
+See the tests folder for examples of how to use this library.
+
 API documentation can be found at [http://hexdocs.pm/credit_card](http://hexdocs.pm/credit_card)
 
+### Using with Phoenix and Ecto
+
+```elixir
+defmodule MyApp.Card do
+  use MyApp.Web, :model
+
+  schema "cards" do
+    field :card_number, :integer
+    field :name_on_card, :string
+    field :valid_from, Ecto.Date
+    field :expires, Ecto.Date
+    timestamps
+  end
+
+  @required_fields ~w(card_number name_on_card valid_from expires)
+  @optional_fields ~w()
+
+  @doc """
+  Creates a changeset based on the `model` and `params`.
+
+  If no params are provided, an invalid changeset is returned
+  with no validation performed.
+  """
+  def changeset(model, params \\ :empty) do
+    model
+    |> cast(params, @required_fields, @optional_fields)
+    |> validate_credit_card(:card_number)
+  end
+
+  def validate_credit_card(changeset, field \\ :card_number, opts \\ []) do
+    validate_change changeset, field, fn _field, number ->
+      message = opts[:message] || "Invalid credit card number"
+      if CreditCard.valid?(to_string(number)) do
+        []
+      else
+        [field, message]
+      end
+    end
+  end
+end
+```
+
 ## TODO
 
 Incorporate some ideas from [Card](https://github.com/jessepollak/card)
@@ -24,5 +68,5 @@ The package can be installed as:
   1. Add credit_card to your list of dependencies in `mix.exs`:
 
         def deps do
-          [{:credit_card, "~> 0.0.1"}]
+          [{:credit_card, "~> 1.0.0"}]
         end