[day-04] add training schema

With this we can represent a traning program for a user.

lib/wabanex/user.ex

@@ -3,6 +3,8 @@ defmodule Wabanex.User do
 
   import Ecto.Changeset
 
+  alias Wabanex.Training
+
   @primary_key {:id, :binary_id, autogenerate: true}
 
   @fields ~w(name email password)a
@@ -12,6 +14,8 @@ defmodule Wabanex.User do
     field :email, :string
     field :password, :string
 
+    has_many :trainings, Training
+
     timestamps()
   end