Added Intercom code snippet

chapter15-1
Sending custom user data.

chapter15-2
Enabling secure mode.

chapter15-3
Displaying the inbox link.

chapter15-4
Hello world for server-side routing.

chapter16-1
Created RSS package, use it to create a rudimentary feed.

chapter16-2
List each post in the feed.

chapter16-3
Added an RSS link to the site header

chapter16-4
Built a simple /api/posts route

chapter16-5
Basic route for showing a post

chapter16-6