Add _drafts to site structure page

site/docs/structure.md

@@ -19,6 +19,9 @@ A basic Jekyll site usually looks something like this:
 {% highlight bash %}
 .
 ├── _config.yml
+├── _drafts
+|   ├── begin-with-the-crazy-ideas.textile
+|   └── on-simplicity-in-technology.markdown
 ├── _includes
 |   ├── footer.html
 |   └── header.html