To index.html.haml add "Comment" link.
Add blank 'show.html.haml' view to app/posts/views
Update 'show' action in PostsController

 * Make instance variable @post available for the show.html.haml view.
Add page header. Also add post author, title and content fields.

 * Also add link "Ignore Comment, Return to Post List"
Generate Comment model.

 * The model is not configured.
 * Command run: Rails generate model Comment author:string content:text
Define relationships between Posts and Comments.

 * A Comment belongs_to one Post.
 * A Post has_many Comments.
Update xxx_create_comments.rb migration to 'reference :post'

 * Run migration: rake db:migrate