Add comment for keyCode 13

keyCode 13 is the 'Enter' button.

Change-Id: I49d6fc00b8e009835b93ed1f62f7f22be083216e
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/app/login/controllers/login-controller.js b/app/login/controllers/login-controller.js
index 45e5a3b..eb8e303 100644
--- a/app/login/controllers/login-controller.js
+++ b/app/login/controllers/login-controller.js
@@ -16,6 +16,8 @@
       $scope.host = $scope.dataService.host.replace(/^https?\:\/\//ig, '');
 
       $scope.tryLogin = function(host, username, password, event) {
+        // keyCode 13 is the 'Enter' button. If the user hits 'Enter' while in
+        // one of the 3 fields, attempt to log in.
         if (event.keyCode === 13) {
           $scope.login(host, username, password);
         }