docs: fix/improve the structure of several documents

Change-Id: Ib8acd4bf29baf19b78d25cabc1a873eeeec15da6
diff --git a/docs/examples.rst b/docs/examples.rst
index cdc2df2..9185caf 100644
--- a/docs/examples.rst
+++ b/docs/examples.rst
@@ -1,7 +1,7 @@
 Trivial applications
 ====================
 
-.. note::
+.. important::
 
     To successfully run the following examples, please make sure that NFD is properly
     configured and running.  For more information about NFD, refer to `NFD's official