Re-instate blockquotes for note.

Author: weierophinney

doc/book/middleware.md

@@ -53,10 +53,10 @@ $route = Literal::factory([
 
 Middleware may be provided as PHP callables, or as service names.
 
-### No action required
-
-Unlike action controllers, middleware typically is single purpose, and, as
-such, does not require a default `action` parameter.
+> ### No action required
+> 
+> Unlike action controllers, middleware typically is single purpose, and, as
+> such, does not require a default `action` parameter.
 
 ## Middleware services