add usage in README file

README.md

@@ -1,20 +1,36 @@
 # Gravatar
 
-**TODO: Add description**
+Gravatar URLs module for Elixir.
 
 ## Installation
 
-If [available in Hex](https://hex.pm/docs/publish), the package can be installed as:
+```elixir
+def deps do
+  [{:gravatar, "~> 0.0.1"}]
+end
+```
 
-  1. Add gravatar to your list of dependencies in `mix.exs`:
+## Usage
 
-        def deps do
-          [{:gravatar, "~> 0.0.1"}]
-        end
+```elixir
+iex(1)> Gravatar.new("test@example.com") |> to_string
+"http://www.gravatar.com/avatar/55502f40dc8b7c769880b10874abc9d0"
 
-  2. Ensure gravatar is started before your application:
+iex(2)> Gravatar.new("test@example.com") |> Gravatar.size(500) |> to_string
+"http://www.gravatar.com/avatar/55502f40dc8b7c769880b10874abc9d0?s=500"
 
-        def application do
-          [applications: [:gravatar]]
-        end
+iex(3)> Gravatar.new("test@example.com") |> Gravatar.size(500) |> Gravatar.secure |> to_string
+"https://www.gravatar.com/avatar/55502f40dc8b7c769880b10874abc9d0?s=500"
+```
 
+## Author
+
+* [Andrea Franz](http://gravityblast.com)
+
+## Contributing
+
+1. Fork it
+2. Create your feature branch (`git checkout -b my-new-feature`)
+3. Commit your changes (`git commit -am 'Add some feature'`)
+4. Push to the branch (`git push origin my-new-feature`)
+5. Create new Pull Request