Minor Markdown consistency changes.

docs/4.0/extend/icons.md

@@ -8,6 +8,7 @@ group: extend
 Bootstrap doesn't include an icon library by default, but we have a handful of recommendations for you to choose from. While most icon sets include multiple file formats, we prefer SVG implementations for their improved accessibility and vector support.
 
 ## Preferred
+
 We've tested and used these icon sets ourselves.
 
 - [Iconic](https://useiconic.com/open/)
@@ -15,6 +16,7 @@ We've tested and used these icon sets ourselves.
 - [Entypo](http://www.entypo.com/)
 
 ## More options
+
 While we haven't tried these out, they do look promising and provide multiple formats—including SVG.
 
 - [Bytesize](https://github.com/danklammer/bytesize-icons)

docs/4.0/extend/index.md

@@ -3,4 +3,4 @@ layout: docs
 title: Extend
 ---
 
-todo: this entire page
+todo: this entire page