Update getting_started.md

- change single quotes to double quotes
- pass article as a local variable instead of instance varialbe in `comments/_form.html.erb`

Author: jcbages

guides/source/getting_started.md

@@ -1655,7 +1655,7 @@ Let us also move that new comment section out to its own partial. Again, you
 create a file `app/views/comments/_form.html.erb` containing:
 
 ```html+erb
-<%= form_with model: [ @article, @article.comments.build ] do |form| %>
+<%= form_with model: [ article, article.comments.build ] do |form| %>
   <p>
     <%= form.label :commenter %><br>
     <%= form.text_field :commenter %>
@@ -1689,17 +1689,14 @@ Then you make the `app/views/articles/show.html.erb` look like the following:
 <%= render @article.comments %>
 
 <h2>Add a comment:</h2>
-<%= render 'comments/form' %>
+<%= render "comments/form", article: @article %>
 ```
 
 The second render just defines the partial template we want to render,
 `comments/form`. Rails is smart enough to spot the forward slash in that
 string and realize that you want to render the `_form.html.erb` file in
 the `app/views/comments` directory.
 
-The `@article` object is available to any partials rendered in the view because
-we defined it as an instance variable.
-
 ### Using Concerns
 
 Concerns are a way to make large controllers or models easier to understand and manage. This also has the advantage of reusability when multiple models (or controllers) share the same concerns. Concerns are implemented using modules that contain methods representing a well-defined slice of the functionality that a model or controller is responsible for. In other languages, modules are often known as mixins.