Show “or email address” in the placeholder for the username box

static/directives/signin-form.html

@@ -1,7 +1,7 @@
 <div class="signin-form-element">
   <form class="form-signin" ng-submit="signin();">
     <input type="text" class="form-control input-lg" name="username"
-           placeholder="Username" ng-model="user.username" autofocus>
+           placeholder="Username or E-mail Address" ng-model="user.username" autofocus>
     <input type="password" class="form-control input-lg" name="password"
            placeholder="Password" ng-model="user.password">
     <button class="btn btn-lg btn-primary btn-block" type="submit">Sign In</button>